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[Alexei A. Belik](https://orcid.org/0000-0001-9031-2355)

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[A Site-Ordered Quadruple Perovskites, RMn3Ni2Mn2O12 with R = Bi, Ce, and Ho, with Different Degrees of B Site Ordering](https://mdr.nims.go.jp/datasets/108ce267-7918-4eac-8e1a-965bc5c4e402)

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A Site-Ordered Quadruple Perovskites, RMn3Ni2Mn2O12 with R = Bi, Ce, and Ho, with Different Degrees of B Site OrderingAcademic Editor: Takashiro AkitsuReceived: 27 March 2025Revised: 10 April 2025Accepted: 11 April 2025Published: 14 April 2025Citation: Belik, A.A. A Site-OrderedQuadruple Perovskites,RMn3Ni2Mn2O12 with R = Bi, Ce, andHo, with Different Degrees of B SiteOrdering. Molecules 2025, 30, 1749.https://doi.org/10.3390/molecules30081749Copyright: © 2025 by the author.Licensee MDPI, Basel, Switzerland.This article is an open access articledistributed under the terms andconditions of the Creative CommonsAttribution (CC BY) license(https://creativecommons.org/licenses/by/4.0/).ArticleA Site-Ordered Quadruple Perovskites, RMn3Ni2Mn2O12 withR = Bi, Ce, and Ho, with Different Degrees of B Site OrderingAlexei A. BelikResearch Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS),Namiki 1-1, Tsukuba 305-0044, Ibaraki, Japan; alexei.belik@nims.go.jpAbstract: A site-ordered quadruple perovskites, AA′3B4O12, can have 3d transition metalsat A′ and B sites, and show complex magnetic interactions and behavior. Additionalcomplexity appears when B site-ordered arrangements are realized in AA′3B2B′2O12. Inthis work, A site-ordered quadruple perovskites, RMn3Ni2Mn2O12 with R = Bi, Ce, andHo, were prepared by a high-pressure, high-temperature method at about 6 GPa and about1500 K. The R = Bi and Ce samples were found to crystallize in space group Im-3 with adisordered distribution of Ni2+ and Mn4+ cations in one B site. On the other hand, theR = Ho sample crystallized in space group Pn-3 and showed partial ordering of Ni2+ andMn4+ cations between two B sites. The structural data (and bond valence sums) suggestthat cerium has the oxidation state +3, which is unusual for such perovskites. Magneticproperties were investigated by magnetic susceptibility and specific heat measurements,which showed the presence of one magnetic transition near 36 K for R = Bi; there wasevidence for the presence of two magnetic transitions near 27 K and 33 K for R = Ce, andnear 10 K and 36 K for R = Ho. Curie–Weiss parameters were estimated for all samplesfrom high-temperature magnetic measurements up to 750 K. The total effective magneticmoment for R = Ce also suggests the presence of Ce3+. A magnetic field of 90 kOe had thelargest effect on the specific heat of the R = Ho sample, and almost no effects on the specificheat of the R = Bi sample.Keywords: A site-ordered quadruple perovskites; B site double ordering; crystal structures;structural disorder; magnetic properties1. IntroductionSimple perovskite oxides, ABO3, usually have non-magnetic A cations (such as, Ca2+,Sr2+, Ba2+, Pb2+, La3+, Y3+, and Bi3+) or magnetic rare-earth cations [1–5]. Therefore, themagnetism of ABO3 perovskites is primarily driven by B cations (if they are magnetic).Even if both A and B cations are magnetic, they behave separately at higher temperatures,and the interaction between A and B cations is weak. For example, RFeO3 perovskites haveFe3+ ordering at about 600–740 K, while R3+ ordering takes place below about 10 K [6].On the other hand, A site-ordered quadruple perovskites, AA′3B4O12, have a smallsquare-planar A′ site, which usually accommodates 3d transition metals [7–11]. Therefore,such perovskites can show complex magnetic interactions and behavior and much strongerinteractions between cations in the A′ and B sites. Additional complexity can appear whendifferent cations are located at the B sites. Depending on the size and charge difference [2],B site-ordered arrangements can be realized, leading to the general formula for suchperovskites being AA′3B2B′2O12 [12–28]. High degrees of B site cation orders are usuallyrealized when the charge difference between B and B′ cations is higher than 3, or whenMolecules 2025, 30, 1749 https://doi.org/10.3390/molecules30081749https://doi.org/10.3390/molecules30081749https://doi.org/10.3390/molecules30081749https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://www.mdpi.com/journal/moleculeshttps://www.mdpi.comhttps://orcid.org/0000-0001-9031-2355https://doi.org/10.3390/molecules30081749https://www.mdpi.com/article/10.3390/molecules30081749?type=check_update&version=1Molecules 2025, 30, 1749 2 of 16there is a large difference in the electronic properties between B and B′ cations [2]. Whenthe charge difference between B and B′ cations is equal to 2, synthesis conditions start toplay a very important role in the degree of cation order [2].Special attention has been given in the literature to perovskite-related compoundswith B = Ni2+ and B′ = Mn4+ [29–46], because such a combination is expected to giveferromagnetic (FM) interactions according to the Goodenough–Kanamori rules [47]. Thecharge difference between Ni2+ and Mn4+ is 2; therefore, it is often challenging to obtainfully ordered samples.Simple R2NiMnO6 perovskites can be prepared at ambient pressure from R = La toR = Lu. The degree of Ni2+ and Mn4+ ordering has significant effects on the FM propertiesof R2NiMnO6 [35–38] and on the saturation magnetization values. In nearly orderedsamples, TC (TC is an FM Curie temperature) decreases almost linearly from 280 K forR = La [30,36] to 40 K for to R = Lu [12,44,45]. Such changes in TC correlate with changesin the Ni–O–Mn bond angles. Further reduction in the Ni–O–Mn bond angle results indramatic changes in magnetic interactions and properties. For example, Sc2NiMnO6, evenwith full ordering of Ni2+ and Mn4+, shows two antiferromagnetic (AFM) transitions anda complex magnetodielectric response [41]. In2NiMnO6, also with full ordering of Ni2+and Mn4+, demonstrates a complex incommensurate AFM structure below TN = 26 K (TNis an AFM Néel temperature) and spin-induced ferroelectric polarization at TN [39,40].As Lu2NiMnO6 appears to be located near a phase boundary between FM and AFMground states, a moderate pressure can change Ni–O–Mn bond angles enough to induce atransition from an FM ground state to an incommensurate AFM ground state [44]. It shouldbe noted that Sc2NiMnO6 and In2NiMnO6 can only be prepared using a high-pressure,high-temperature method.Peculiarities of both the R2NiMnO6 and AA′3B2B′2O12 perovskite families are com-bined in the case of LaMn3Ni2Mn2O12 [12], which can be prepared only using a high-pressure, high-temperature method. LaMn3Ni2Mn2O12 is located in a region of a phasediagram with unusual properties similar to those of Sc2NiMnO6 and In2NiMnO6. Forexample, two magnetic transitions were found in LaMn3Ni2Mn2O12 at 34 K and 46 Kwith original magnetic structures [12,13]. Such perovskites were recently extended toRMn3Ni2Mn2O12 with R = Nd, Sm, Gd, and Dy [48], which can also be prepared only usinga high-pressure, high-temperature method.In this work, we investigated RMn3Ni2Mn2O12 with R = Bi, Ce, and Ho. Bi-containingperovskites are exceptional members of any perovskite family [49–53] in the majority ofcases, as a Bi3+ cation has the lone electron pair and promotes polar distortions. Ce usuallyhas the oxidation state of +4; therefore, Ce-containing members of any perovskite familymay differ from other members of the same series with R3+. Perovskites with differentoxidation states of Ce are reported in the literature [54–62]. Ho3+ is the smallest cation forwhich RMn3Ni2Mn2O12 perovskites have been prepared so far.2. Results and DiscussionAll prepared RMn3Ni2Mn2O12 samples with R = Bi, Ce, and Ho had a cubic crystalstructure, as all reflections belonging to RMn3Ni2Mn2O12 could be indexed in a cubicsystem. The samples also contained different impurities depending on R: the R = Bi samplehad Bi2O2CO3, NiO, NiMnO3, and GdFeO3-type impurities, the R = Ce had CeO2, NiO, andNiMnO3 impurities, and the R = Ho sample had HoMn2O5, NiO, and NiMnO3 impurities.All cubic reflections of the R = Bi and Ce samples could be indexed in space group Im-3,which is the parent (maximum) symmetry of the AA′3B4O12-type perovskites [7–11]. Onthe other hand, a (311) reflection was observed in the synchrotron XRPD data of the R = Hosample (the inset of Figure 1a). This reflection is forbidden in space group Im-3, andMolecules 2025, 30, 1749 3 of 16suggests space group Pn-3, which is observed in cases of full or partial B site ordering ofAA′3B2B′2O12-type perovskites [12,14–19].Molecules 2025, 30, x FOR PEER REVIEW 3 of 17   suggests space group Pn-3, which is observed in cases of full or partial B site ordering of AA′3B2B′2O12-type perovskites [12,14–19].  Figure 1. Fragments of experimental (black crosses), calculated (red line), and difference (blue line at the bottom) room-temperature synchrotron X-ray powder diffraction patterns of (a) HoMn3Ni2Mn2O12 (the Pn-3 modification) and (b) CeMn3Ni2Mn2O12 (the Im-3 modification) in a 2θ range of 5° and 50°. The tick marks show possible Bragg reflection positions for the main phase (black) and impurities (from top to bottom for HoMn2O5 (blue), NiO (green), and NiMnO3 (brown) for R = Ho and for CeO2 (blue), NiO (green), and NiMnO3 (brown) for R = Ce). Insets show magnified parts in a 2θ range of 15° and 17°, and emphasize the presence of the (311) reflection for R = Ho from the B site ordering and the absence of such a reflection for R = Ce. The distribution of Ni2+ and Mn4+ cations between the B and B′ sites in the R = Ho sample was refined with the following constraints: (1) the full site occupation, g(Mn) + g(Ni) = 1, where g is the occupation factor, should be kept, and (2) the total chemical com-position should be kept. The obtained distribution of Ni2+ and Mn4+ cations was close to 0.8Ni2+ + 0.2Mn4+ for the B site and 0.2Ni2+ + 0.8Mn4+ for the B′ site. These values suggest a significant degree of Ni2+ and Mn4+ ordering. We note that similar distributions of Ni2+ and Mn4+ cations were found in samples with R = Nd, Sm, Gd, and Dy [48] prepared under the same conditions. The refinement of the occupation factors of the R sites (together with atomic displace-ment parameters (ADPs) of the R sites and all other refined parameters) gave the Figure 1. Fragments of experimental (black crosses), calculated (red line), and difference(blue line at the bottom) room-temperature synchrotron X-ray powder diffraction patterns of(a) HoMn3Ni2Mn2O12 (the Pn-3 modification) and (b) CeMn3Ni2Mn2O12 (the Im-3 modification)in a 2θ range of 5◦ and 50◦. The tick marks show possible Bragg reflection positions for the mainphase (black) and impurities (from top to bottom for HoMn2O5 (blue), NiO (green), and NiMnO3(brown) for R = Ho and for CeO2 (blue), NiO (green), and NiMnO3 (brown) for R = Ce). Insets showmagnified parts in a 2θ range of 15◦ and 17◦, and emphasize the presence of the (311) reflection forR = Ho from the B site ordering and the absence of such a reflection for R = Ce.The distribution of Ni2+ and Mn4+ cations between the B and B′ sites in the R = Ho sam-ple was refined with the following constraints: (1) the full site occupation, g(Mn) + g(Ni) = 1,where g is the occupation factor, should be kept, and (2) the total chemical composi-tion should be kept. The obtained distribution of Ni2+ and Mn4+ cations was close to0.8Ni2+ + 0.2Mn4+ for the B site and 0.2Ni2+ + 0.8Mn4+ for the B′ site. These values suggesta significant degree of Ni2+ and Mn4+ ordering. We note that similar distributions of Ni2+and Mn4+ cations were found in samples with R = Nd, Sm, Gd, and Dy [48] prepared underthe same conditions.The refinement of the occupation factors of the R sites (together with atomic displace-ment parameters (ADPs) of the R sites and all other refined parameters) gave the followingvalues: g(Bi) = 1.0001(13), g(Ce) = 0.9710(15), and g(Ho) = 0.9929(14). These values wereMolecules 2025, 30, 1749 4 of 16close to 1 within the sensitivity of the method, as such deviations could be absorbed byreasonable ADPs. Therefore, we fixed the occupation factor of the R sites at 1 in the finalreported models. We emphasize that the ADP for Bi was enhanced. However, all attemptsto split (to reduce the ADP of Bi) the Bi site from the ideal (0, 0, 0) position to differentpositions failed. Enhanced ADPs for Bi are often observed in such perovskites with a cubicstructure, even in neutron diffraction data [52]. Enhanced ADPs for Bi are caused by theeffect of the lone electron pair of Bi3+ cations and random displacements of Bi3+ cations.The refined structural parameters of HoMn3Ni2Mn2O12 are summarized in Table 1,and those of RMn3Ni2Mn2O12 with R = Bi and Ce in Table 2. Experimental, calculated,and difference synchrotron X-ray powder diffraction patterns are shown in Figure 1 forHoMn3Ni2Mn2O12 and CeMn3Ni2Mn2O12. Figure S1 gives experimental, calculated, anddifference synchrotron X-ray powder diffraction patterns for BiMn3Ni2Mn2O12.Table 1. Structural parameters of HoMn3Ni2Mn2O12 (Pn-3; prepared at 1500 K) at room temperaturefrom synchrotron powder X-ray diffraction data.Site WP g x y z Biso (Å2)Ho 2a 1 0.25 0.25 0.25 0.685(6)MnSQ 6d 1 0.25 0.75 0.75 0.507(9)Ni1/Mn1 4b 0.815(12)Ni + 0.185Mn 0 0 0 0.31(3)Mn2/Ni2 4c 0.815Mn + 0.185Ni 0.5 0.5 0.5 0.29(3)O 24h 1 0.2578(4) 0.4242(2) 0.5567(2) 0.56(3)Note. Crystal system: cubic; space group Pn-3 (No. 201, setting 2); Z = 2. Source: synchrotron powder X-raydiffraction (λ = 0.6200666 Å); d-space range used in refinements: 0.4678–7.108 Å. a = 7.32452(1) Å, V = 392.9504(9)Å3. WP: Wyckoff position. Rwp = 9.24%, Rp = 6.29%, RI = 2.48%, and RF = 2.35% after background subtraction.Rwp = 6.34%, Rp = 4.62%, RI = 3.16%, and RF = 3.49% without background subtraction. Occupation factors, g, ofHo, MnSQ, and O sites are 1. Constraints on occupation factors: g(Mn1) = g(Ni2) = 1 − g(Ni1) and g(Mn2) = g(Ni1).Impurities: NiO—2.5 wt. %, HoMn2O5—3.2 wt. %, and NiMnO3—0.4 wt. %.The bond valence sum (BVS) values [63,64] of the MnSQ site (where SQ stands forsquare-planar) were close to +3 for all three compounds (+2.94 for R = Bi, +2.97 for R = Ce,and +2.95 for R = Ho) suggesting that this site is occupied by Mn3+ cations. The BVSvalues of the Ni/Mn site (with R0 = 1.7035, which is the average value of R0(Ni2+) andR0(Mn4+) [63]) were +2.90 for R = Bi and +2.89 for R = Ce, again close to the averageoxidation state of Ni2+ and Mn4+ cations. On the other hand, for R = Ho, the BVS value ofthe Ni1/Mn1 site (with the majority of Ni2+) was +2.28, and the BVS value of the Mn2/Ni2site (with the majority of Mn4+) was +3.98, in agreement with the expected values. The BVSvalue of the Ni1/Mn1 site was somewhat higher than +2; however, similar values wereobserved in all other members of the RMn3Ni2Mn2O12 family with R = La [12], Nd, Sm,Gd, and Dy [48].The BVS values of the R site were +2.71 for R = Bi, +3.04 for R = Ce [64], and +2.63for R = Ho. Reduced BVS values of Bi3+ cations are often observed in Bi-containing Asite-ordered quadruple perovskites [49,52], and could be caused by the influence of thelone electron pair of Bi3+ cations. The BVS value for Ho3+ suggests that Ho3+ cations arehighly underbonded inside the A site. The severe underbonding could be a reason whyRMn3Ni2Mn2O12 compounds become unstable with smaller R3+ cations [65], such as withR = Er-Lu [48], under the synthesis conditions used. In RMn3Ni2Mn2O12, the BVS values ofR3+ cations changed from +3.40 for R = La [12] to +2.72 for R = Dy [48]. Therefore, the BVSvalue for R = Ho agrees with the general tendency in such perovskites. These BVS valuesalso suggest that cations at the A site can be highly overbonded or highly underbonded,but the structure can still tolerate such stress. Stabilization of the structure was realizedthrough the high-pressure, high-temperature preparation method. The BVS value for Cesuggests that Ce has an oxidation state of +3. Therefore, the reduction of Ce4+ (added asMolecules 2025, 30, 1749 5 of 16CeO2) took place during the synthesis of CeMn3Ni2Mn2O12, and CeMn3Ni2Mn2O12 is notan exceptional member of the R3+Mn3Ni2Mn2O12 series. The reduction of Ce4+ occurredthrough the oxidation of a part of Mn3+, as the high-pressure synthesis was performed insealed capsules in closed environment.Table 2. Structural parameters of RMn3Ni2Mn2O12 (Im-3; prepared at 1500 K) at room temperaturefrom synchrotron powder X-ray diffraction data.R Bi CeWavelength (Å) 0.4137875 0.6200666Used d-space range (Å) 0.3122–11.855 0.4678–7.108a (Å) 7.37294(1) 7.37071(1)V (Å3) 400.7949(11) 400.4314(7)Biso(R) (Å2) 2.095(9) 0.565(9)Biso(MnSQ) (Å2) 0.624(12) 0.521(12)Biso(Ni/Mn) (Å2) 0.436(8) 0.280(9)x(O) 0.31118(22) 0.31053(20)y(O) 0.17728(24) 0.17562(22)Biso(O) (Å2) 0.83(4) 0.62(3)Rwp (%) 7.54 (6.22) 8.48 (6.76)Rp (%) 5.37 (4.56) 5.73 (4.96)RI (%) 3.37 (3.49) 2.87 (3.67)RF (%) 5.99 (6.03) 1.58 (2.59)Impurities:NiO 1.9 wt. % 2.5 wt. %Bi2O2CO3 1.4 wt. % -NiMnO3 2.0 wt. % 5.7 wt. %CeO2 - 3.4 wt. %GdFeO3-type 0.5 wt. % -Note. Crystal system: cubic; space group Im-3 (No. 204); Z = 2. Fractional coordinates: R: 2a (0, 0, 0), MnSQ: 6b(0, 0.5, 0.5), Ni/Mn: 8c (0.25, 0.25, 0.25), and O: 24g (x, y, 0). Occupation factors, g, of R, MnSQ, and O sites are1. Occupation of Ni/Mn site was fixed at 0.5Ni + 0.5Mn. R values are given after background subtraction; Rvalues in parenthesis are without background subtraction. For GdFeO3-type impurity in R = Bi, a = 5.5767 Å,b = 7.7491 Å, and c = 5.4052 Å.The results of the specific heat measurements are given in Figures 2–4. None of thesamples showed sharp peaks on specific heat curves. Nevertheless, clear anomalies were ob-served that could be assigned to long-range magnetic orderings. BiMn3Ni2Mn2O12 showeda clear kink at 36 K (Figure 2), below which the Cp/T values started decreasing sharply.High magnetic fields (up to 90 kOe) had almost no effects on the specific heat values ofBiMn3Ni2Mn2O12, suggesting that the magnetic state was quite robust. CeMn3Ni2Mn2O12showed a broadened kink at 33 K (Figure 3) and a second kink at 27 K, below which theCp/T values started decreasing. High magnetic fields (up to 90 kOe) had weak effectson the specific heat values of CeMn3Ni2Mn2O12, and moved the positions of the broadanomaly to slightly higher temperatures. HoMn3Ni2Mn2O12 showed two broadened peaksnear 36 K and 10 K (Figure 4). High magnetic fields (up to 90 kOe) noticeably smeared theanomaly near 10 K, and moved the positions of the second broad anomaly to slightly lowertemperatures. The specific heat data of HoMn3Ni2Mn2O12 were very close to the specificheat curves of DyMn3Ni2Mn2O12 [48].Molecules 2025, 30, 1749 6 of 16Molecules 2025, 30, x FOR PEER REVIEW 6 of 17   slightly lower temperatures. The specific heat data of HoMn3Ni2Mn2O12 were very close to the specific heat curves of DyMn3Ni2Mn2O12 [48].  Figure 2. Cp/T versus T curves of BiMn3Ni2Mn2O12 measured at H = 0 (black curves) and 90 kOe (red curves). The inset shows Cp/T versus T curves at H = 0, 10, 30, 50, and 70 kOe. The arrow shows the magnetic transition temperature.  Figure 2. Cp/T versus T curves of BiMn3Ni2Mn2O12 measured at H = 0 (black curves) and 90 kOe(red curves). The inset shows Cp/T versus T curves at H = 0, 10, 30, 50, and 70 kOe. The arrow showsthe magnetic transition temperature.Molecules 2025, 30, x FOR PEER REVIEW 6 of 17   slightly lower temperatures. The specific heat data of HoMn3Ni2Mn2O12 were very close to the specific heat curves of DyMn3Ni2Mn2O12 [48].  Figure 2. Cp/T versus T curves of BiMn3Ni2Mn2O12 measured at H = 0 (black curves) and 90 kOe (red curves). The inset shows Cp/T versus T curves at H = 0, 10, 30, 50, and 70 kOe. The arrow shows the magnetic transition temperature.  Figure 3. Cp/T versus T curves of CeMn3Ni2Mn2O12 measured at H = 0 (black curves) and 90 kOe(red curves). The inset shows Cp/T versus T curves at H = 0, 10, 30, 50, and 70 kOe. The arrows showmagnetic transition temperatures.Molecules 2025, 30, 1749 7 of 16Molecules 2025, 30, x FOR PEER REVIEW 7 of 17   Figure 3. Cp/T versus T curves of CeMn3Ni2Mn2O12 measured at H = 0 (black curves) and 90 kOe (red curves). The inset shows Cp/T versus T curves at H = 0, 10, 30, 50, and 70 kOe. The arrows show magnetic transition temperatures.  Figure 4. Cp/T versus T curves of HoMn3Ni2Mn2O12 measured at H = 0 (black curves) and 90 kOe (red curves). The inset shows Cp/T versus T curves at H = 0, 10, 30, 50, and 70 kOe. The arrows show magnetic transition temperatures. The temperature dependence of the magnetic susceptibility of BiMn3Ni2Mn2O12 is shown in Figure 5a, and Figure 5b gives an M versus H curve at 5 K, 60 K, and 300 K. The divergence between the ZFC and FCC curves was observed below about 15 K at H = 10 kOe; at the same temperature, a broad maximum was observed on the ZFC curve. How-ever, no clear anomalies were detected near 36 K, even on differential curves. Therefore, only specific heat data could clearly identify a magnetic phase transition temperature in BiMn3Ni2Mn2O12. The M versus H curves showed a very weak step-like hysteresis near the origin. The hysteresis near the origin probably originated from a small amount of fer-rimagnetic NiMnO3 impurity (with TC = 430 K [66]) with soft ferrimagnetic properties, as the hysteresis was observed even at 300 K. A slim extended hysteresis observed at 5 K (the inset of Figure 5b) originated from BiMn3Ni2Mn2O12. Figure 4. Cp/T versus T curves of HoMn3Ni2Mn2O12 measured at H = 0 (black curves) and 90 kOe(red curves). The inset shows Cp/T versus T curves at H = 0, 10, 30, 50, and 70 kOe. The arrows showmagnetic transition temperatures.The temperature dependence of the magnetic susceptibility of BiMn3Ni2Mn2O12 isshown in Figure 5a, and Figure 5b gives an M versus H curve at 5 K, 60 K, and 300 K.The divergence between the ZFC and FCC curves was observed below about 15 K atH = 10 kOe; at the same temperature, a broad maximum was observed on the ZFC curve.However, no clear anomalies were detected near 36 K, even on differential curves. Therefore,only specific heat data could clearly identify a magnetic phase transition temperature inBiMn3Ni2Mn2O12. The M versus H curves showed a very weak step-like hysteresis nearthe origin. The hysteresis near the origin probably originated from a small amount offerrimagnetic NiMnO3 impurity (with TC = 430 K [66]) with soft ferrimagnetic properties,as the hysteresis was observed even at 300 K. A slim extended hysteresis observed at 5 K(the inset of Figure 5b) originated from BiMn3Ni2Mn2O12.The temperature dependence of the magnetic susceptibility of CeMn3Ni2Mn2O12 isshown in Figure 6a, and Figure 6b gives an M versus H curve at 5 K, 60 K, and 300 K. Thedivergence between the ZFC and FCC curves was observed below about 10 K at H = 10 kOe;at nearly the same temperature, a broad maximum was observed on the ZFC curve. Thedifferential curves showed some anomalies; for example, the dχT/dT versus T curves atH = 100 Oe showed peaks at 27 K with shoulders at 33 K, in agreement with the specificheat data; on the other hand, at H = 10 kOe, only one broad anomaly was seen at 33 K. TheM versus H curve at 5 K demonstrated a slim extended hysteresis. Above TN (at 60 K and300 K), a very weak, step-like hysteresis was observed near the origin, originating fromferrimagnetic NiMnO3 impurity [66]. Therefore, the extended hysteresis at 5 K shouldoriginate from the main phase.Molecules 2025, 30, 1749 8 of 16Molecules 2025, 30, x FOR PEER REVIEW 8 of 17    Figure 5. (a) ZFC (filled symbols) and FCC (empty symbols) dc magnetic susceptibility curves (χ = M/H) of BiMn3Ni2Mn2O12 measured at H = 10 kOe. (b) M versus H curves of BiMn3Ni2Mn2O12 at T = 5 K, 60 K, and 300 K. The inset shows magnified parts near the origin. The temperature dependence of the magnetic susceptibility of CeMn3Ni2Mn2O12 is shown in Figure 6a, and Figure 6b gives an M versus H curve at 5 K, 60 K, and 300 K. The divergence between the ZFC and FCC curves was observed below about 10 K at H = 10 kOe; at nearly the same temperature, a broad maximum was observed on the ZFC curve. The differential curves showed some anomalies; for example, the dχT/dT versus T curves at H = 100 Oe showed peaks at 27 K with shoulders at 33 K, in agreement with the specific heat data; on the other hand, at H = 10 kOe, only one broad anomaly was seen at 33 K. The M versus H curve at 5 K demonstrated a slim extended hysteresis. Above TN (at 60 K and 300 K), a very weak, step-like hysteresis was observed near the origin, originating from ferrimagnetic NiMnO3 impurity [66]. Therefore, the extended hysteresis at 5 K should originate from the main phase. Figure 5. (a) ZFC (filled symbols) and FCC (empty symbols) dc magnetic susceptibility curves(χ = M/H) of BiMn3Ni2Mn2O12 measured at H = 10 kOe. (b) M versus H curves of BiMn3Ni2Mn2O12at T = 5 K, 60 K, and 300 K. The inset shows magnified parts near the origin.The temperature dependence of the magnetic susceptibility of HoMn3Ni2Mn2O12is shown in Figure 7a, and Figure 7b gives M versus H curves at 5 K and 60 K. In thiscase, kinks on the χ versus T curves were clearly observed at 36 K. The differential dχ/dTversus T curves at H = 100 Oe and 10 kOe showed sharp anomalies at 36 K and broaderanomalies near 10 K, in agreement with the specific heat data. The M versus H curvesshowed almost no hysteresis. No detectable step-like hysteresis was observed near theorigin at 60 K (above TN of HoMn3Ni2Mn2O12) from NiMnO3 impurity, because of its verysmall amount. The χ versus T and M versus H curves of HoMn3Ni2Mn2O12 were veryclose to those of DyMn3Ni2Mn2O12 [48]. The ground states of Ho3+ and Dy3+ cations are, ofcourse, different [67]. Nevertheless, these cations are quite close to each other, as they haveclose ionic radii (rVIII(Dy3+) = 1.027 Å versus rVIII(Ho3+) = 1.015 Å [65]), effective calculatedMolecules 2025, 30, 1749 9 of 16magnetic moments (10.63µB for Dy3+ versus 10.60µB for Ho3+ [67]), and maximum orderedmagnetic moments (of 10µB). Therefore, it could be expected that HoMn3Ni2Mn2O12 andDyMn3Ni2Mn2O12 would have similar magnetic properties and ground states.Molecules 2025, 30, x FOR PEER REVIEW 9 of 17    Figure 6. (a) ZFC (filled symbols) and FCC (empty symbols) dc magnetic susceptibility curves (χ = M/H) of CeMn3Ni2Mn2O12 measured at H = 10 kOe. The inset shows ZFC and FCC dχT/dT versus T curves at H = 100 Oe (black curves) and 10 kOe (blue curves). (b) M versus H curves of CeMn3Ni2Mn2O12 at T = 5 K, 60 K, and 300 K. The inset shows magnified parts near the origin. The temperature dependence of the magnetic susceptibility of HoMn3Ni2Mn2O12 is shown in Figure 7a, and Figure 7b gives M versus H curves at 5 K and 60 K. In this case, kinks on the χ versus T curves were clearly observed at 36 K. The differential dχ/dT versus T curves at H = 100 Oe and 10 kOe showed sharp anomalies at 36 K and broader anomalies near 10 K, in agreement with the specific heat data. The M versus H curves showed almost no hysteresis. No detectable step-like hysteresis was observed near the origin at 60 K (above TN of HoMn3Ni2Mn2O12) from NiMnO3 impurity, because of its very small amount. The χ versus T and M versus H curves of HoMn3Ni2Mn2O12 were very close to those of DyMn3Ni2Mn2O12 [48]. The ground states of Ho3+ and Dy3+ cations are, of course, different [67]. Nevertheless, these cations are quite close to each other, as they have close ionic radii Figure 6. (a) ZFC (filled symbols) and FCC (empty symbols) dc magnetic susceptibility curves(χ = M/H) of CeMn3Ni2Mn2O12 measured at H = 10 kOe. The inset shows ZFC and FCC dχT/dTversus T curves at H = 100 Oe (black curves) and 10 kOe (blue curves). (b) M versus H curves ofCeMn3Ni2Mn2O12 at T = 5 K, 60 K, and 300 K. The inset shows magnified parts near the origin.NiMnO3 is a ferrimagnetic material with a TC of about 430 K [66]. Therefore, it givesnoticeable contributions to the measured magnetic properties in small magnetic fields (suchas 100 Oe (Figure S2)) below 400 K (Figure 8). As NiMnO3 is a soft ferrimagnetic material,its magnetization saturates at high magnetic fields. Therefore, the larger the measurementmagnetic field, the smaller the relative contribution of NiMnO3. However, we foundthat even at 70 kOe (the maximum available magnetic field), contributions from NiMnO3affected parameters of the Curie–Weiss fits below 400 K (Figure 8). Therefore, we performedhigh-temperature magnetic measurements up to 750 K. Above about 440 K, magneticMolecules 2025, 30, 1749 10 of 16susceptibilities were independent of the measurement magnetic field, and reliable, intrinsicCurie–Weiss parameters could be obtained. Inverse magnetic susceptibilities followedthe Curie–Weiss law at high temperatures. The Curie–Weiss fits were performed between480 and 750 K (for the 70 kOe FCC curves), and the resultant parameters are summarizedin Table 3. The experimental effective magnetic moments (µeff) were very close to thecalculated values (µcalc), supporting the charges of magnetic cations. In particular, theinclusion of the magnetic moment of Ce3+ [67] in the calculation gave a better agreementbetween µeff and µcalc; this fact gives indirect support for the +3 oxidation state of Ce, inaddition to the structural data. We note that the Curie–Weiss temperatures (θ) were verysmall for the R = Ce and Ho samples when the fits were performed between 200 K and380 K at 70 kOe (Figure 8).Molecules 2025, 30, x FOR PEER REVIEW 10 of 17   (rVIII(Dy3+) = 1.027 Å versus rVIII(Ho3+) = 1.015 Å [65]), effective calculated magnetic mo-ments (10.63µB for Dy3+ versus 10.60µB for Ho3+ [67]), and maximum ordered magnetic moments (of 10µB). Therefore, it could be expected that HoMn3Ni2Mn2O12 and DyMn3Ni2Mn2O12 would have similar magnetic properties and ground states.  Figure 7. (a) ZFC (filled symbols) and FCC (empty symbols) dc magnetic susceptibility curves (χ = M/H) of HoMn3Ni2Mn2O12 measured at H = 10 kOe. The inset shows ZFC and FCC dχ/dT versus T curves at H = 100 Oe (black curves) and 10 kOe (blue curves). The right-hand axis shows the FCC χ−1 versus T curve. The arrows show the magnetic transition temperatures. (b) M versus H curves of HoMn3Ni2Mn2O12 at T = 5 K and 60 K. The inset shows magnified parts near the origin. NiMnO3 is a ferrimagnetic material with a TC of about 430 K [66]. Therefore, it gives noticeable contributions to the measured magnetic properties in small magnetic fields (such as 100 Oe (Figure S2)) below 400 K (Figure 8). As NiMnO3 is a soft ferrimagnetic material, its magnetization saturates at high magnetic fields. Therefore, the larger the measurement magnetic field, the smaller the relative contribution of NiMnO3. However, we found that even at 70 kOe (the maximum available magnetic field), contributions from Figure 7. (a) ZFC (filled symbols) and FCC (empty symbols) dc magnetic susceptibility curves(χ = M/H) of HoMn3Ni2Mn2O12 measured at H = 10 kOe. The inset shows ZFC and FCC dχ/dTversus T curves at H = 100 Oe (black curves) and 10 kOe (blue curves). The right-hand axis shows theFCC χ−1 versus T curve. The arrows show the magnetic transition temperatures. (b) M versus Hcurves of HoMn3Ni2Mn2O12 at T = 5 K and 60 K. The inset shows magnified parts near the origin.Molecules 2025, 30, 1749 11 of 16Molecules 2025, 30, x FOR PEER REVIEW 12 of 17    Figure 8. Inverse dc magnetic susceptibility curves (χ−1 = H/M) of (a) BiMn3Ni2Mn2O12, (b) CeMn3Ni2Mn2O12, and (c) HoMn3Ni2Mn2O12 measured at H = 100 Oe (brown), 10 kOe (blue), and 70 kOe (black) on cooling (FCC curves) in the low-temperature (LT) region of 2–400 K (circles) and the high-temperature (HT) region of 330–750 K (triangles). The red lines show Curie–Weiss fits (for the 70 kOe data at HT and for the 10 kOe and 70 kOe data at LT); parameters of the fits are given in the figure. RMn3Ni2Mn2O12 samples with R = Bi, Ce, and Ho were prepared under the same syn-thesis conditions (6 GPa and 1500 K). The same synthesis conditions were used for the Figure 8. Inverse dc magnetic susceptibility curves (χ−1 = H/M) of (a) BiMn3Ni2Mn2O12,(b) CeMn3Ni2Mn2O12, and (c) HoMn3Ni2Mn2O12 measured at H = 100 Oe (brown), 10 kOe (blue),and 70 kOe (black) on cooling (FCC curves) in the low-temperature (LT) region of 2–400 K (circles)and the high-temperature (HT) region of 330–750 K (triangles). The red lines show Curie–Weiss fits(for the 70 kOe data at HT and for the 10 kOe and 70 kOe data at LT); parameters of the fits are givenin the figure.Molecules 2025, 30, 1749 12 of 16Table 3. Temperatures of magnetic anomalies and parameters of Curie–Weiss fits and M versus Hcurves at T = 5 K for RMn3Ni2Mn2O12.R (Symmetry) TN (K) µeff (µB/f.u.) µcalc (µB/f.u.) θ (K) MS (µB/f.u.)Bi (Im-3) 36 10.899(2) 10.863 −55.9(3) 2.76Ce (Im-3) 27, 33 11.169(1) 11.125 −40.8(2) 5.42Ho (Pn-3) 10, 36 15.164(2) 15.178 −21.1(1) 11.66The Curie–Weiss fits were performed between 480 K and 750 K using the FCC χ−1 versus T data at 70 kOe. MS isthe magnetization value at T = 5 K and H = 70 kOe. µcalc was calculated using 2.4µB for Ce3+, 10.6µB for Ho3+,4.899µB for Mn3+, 2.828µB for Ni2+, and 3.873µB for Mn4+ [67]. TN values were determined from peaks on the100 Oe and 10 kOe FCC d(χT)/dT versus T or dχ/dT versus T curves, or from specific heat data.RMn3Ni2Mn2O12 samples with R = Bi, Ce, and Ho were prepared under the samesynthesis conditions (6 GPa and 1500 K). The same synthesis conditions were used forthe preparation of RMn3Ni2Mn2O12 with R = Nd, Sm, Gd, and Dy [48]. These conditionsproduced partial ordering of Ni2+ and Mn4+ cations in the case of R = Nd-Ho. It wasalso found that an increase in the synthesis temperature to 1700 K produced sampleswith a disordered arrangement of Ni2+ and Mn4+ cations in the case of R = Nd andSm [48]. Therefore, the disordered arrangement of Ni2+ and Mn4+ cations found in theR = Bi and Ce samples prepared at 1500 K could suggest that a (partial) ordering may berealized at lower synthesis temperatures. This possibility may be explored in the future.Note that larger amounts of impurities in the R = Ce sample (Table 2) could shift thereal chemical composition of the main phase and contribute to the stabilization of thedisordered structure.3. ExperimentalRMn3Ni2Mn2O12 samples with R = Bi, Ce, and Ho were prepared from stoichiometricmixtures of Bi2O3 (Rare Metallic Co., Tokyo, Japan, 99.9999%), CeO2 (Rare Metallic Co.,Tokyo, Japan, 99.99%), Ho2O3 (Rare Metallic Co., Tokyo, Japan, 99.9%), Mn2O3 (RareMetallic Co., Tokyo, Japan, 99.99%), MnO2 (Alfa Aesar, Ward Hill, MA, USA, 99.99%), andNiO (Rare Metallic Co., Tokyo, Japan, 99.9%). Single-phase Mn2O3 was prepared from acommercial MnO2 chemical (Rare Metallic Co., Tokyo, Japan, 99.99%) by annealing in airat 923 K for 24 h. The synthesis was performed at about 6 GPa and at about 1500 K for2 h in sealed Au capsules, using a belt-type HP instrument. After annealing at 1500 K, thesamples were cooled down to room temperature by turning off the heating current, and thepressure was slowly released.X-ray powder diffraction (XRPD) data were collected at room temperature on a Mini-Flex600 diffractometer (Rigaku, Tokyo, Japan) using CuKα radiation (2θ range of 8–100◦,step width of 0.02◦, and scan speed of 2◦/min). Room-temperature synchrotron XRPD datawere measured using the beamline BL02B2 [68,69] of SPring-8, Japan. Intensity data werecollected between 1.00◦ and 83.02◦ at a 0.006◦ interval in 2θ with 100 s exposure time. Awavelength of λ = 0.4137875 Å was used for R = Bi (to reduce the absorption effect becauseof the presence of heavy Bi). A wavelength of λ = 0.6200666 Å was used for R = Ce andHo. The samples were placed into open Lindemann glass capillary tubes (inner diameter:0.2 mm), which were rotated during measurements. The Rietveld analysis of all XRPD datawas performed using the RIETAN-2000 program [70]. Normalized (because of differentmeasurement times) background (obtained through measurements of (different) emptycapillary tubes) was subtracted from the raw synchrotron XRPD data. Background sub-traction usually gives larger profile agreement factors (Rwp and Rp) because backgroundintensities become very low. On the other hand, the background subtraction usually im-proves integrated agreement factors (RI and RF) because better structure descriptions areachieved. The remaining background was fitted by 12-order Legendre polynomials. WeMolecules 2025, 30, 1749 13 of 16note that NiMnO3 impurity was fitted using the ilmenite-type model (space group R-3) inthe R = Bi and Ce samples, and using the simple corundum-type model (space group R-3c)in the R = Ho sample, because of its very small amount.Magnetic measurements were performed on SQUID magnetometers (Quantum DesignMPMS3, San Diego, CA, USA) between 2 and 400 K in applied fields of 100 Oe, 10 kOe, and70 kOe, under both zero-field-cooled (ZFC) and field-cooled on cooling (FCC) conditions.High-temperature magnetic measurements were performed between 330 K and 750 K withthe same magnetic fields using a high-temperature MPMS3 option, where dense pelletsof the samples with polished flat surfaces were attached to a high-temperature stick withZircar cement. Isothermal magnetization was measured at temperatures of 5 K, 60 K, and300 K, between −70 and 70 kOe.The specific heat, Cp, was measured on cooling from 100 K to 2 K at different magneticfields up to 90 kOe by a pulse relaxation method, using a commercial calorimeter (QuantumDesign PPMS, San Diego, CA, USA). All magnetic and specific heat measurements wereperformed using pieces of dense pellets.4. ConclusionsThe synthesis of A site-ordered quadruple perovskites, RMn3Ni2Mn2O12 with R = Bi,Ce, and Ho, was performed by a high-pressure, high-temperature method at about 6 GPaand about 1500 K. Despite using the same synthesis conditions, the R = Bi and Ce samplescrystallized in space group Im-3 with a disordered arrangement of Ni2+ and Mn4+ cations.On the other hand, the R = Ho sample crystallized in space group Pn-3 with partialordering of Ni2+ and Mn4+ cations. By using a combination of magnetic susceptibility andspecific heat measurements, one magnetic transition was detected in the R = Bi sample near36 K. On the other hand, two magnetic transitions were found near 27 K and 33 K in theR = Ce sample, and near 10 K and 36 K in the R = Ho sample. Magnetic properties wereaffected by the presence of ferrimagnetic NiMnO3 impurity (with a TC of about 430 K).Therefore, Curie–Weiss parameters were estimated for all samples from high-temperaturemagnetic measurements up to 750 K. The total effective magnetic moment for R = Ceand structural information, obtained from the state-of-the-art synchrotron X-ray powderdiffraction, suggested the presence of Ce3+.Supplementary Materials: The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/molecules30081749/s1: Figure S1: Fragments (between 3◦ and25◦) and magnified parts of experimental, calculated, and difference synchrotron X-ray powderdiffraction patterns of BiMn3Ni2Mn2O12 at T = 297 K; Figure S2: ZFC and FCC magnetic susceptibilitycurves of RMn3Ni2Mn2O12 with R = Bi, Ce, and Ho at H = 100 Oe, between 330 K and 550 K.Funding: This research received no external funding.Institutional Review Board Statement: Not applicable.Informed Consent Statement: Not applicable.Data Availability Statement: The raw data supporting the conclusions of this article will be madeavailable by the author upon request.Acknowledgments: Synchrotron radiation experiments were conducted on the powder diffractionbeamline BL02B2 at SPring-8, with the permission from the Japan Synchrotron Radiation ResearchInstitute (Proposal Number: 2024B1825). The author thanks Y. Mori for his help with BL02B2 ofSPring-8, and R. Liu for her preliminary studies of RMn3Ni2Mn2O12 compounds. MANA wassupported by the World Premier International Research Center Initiative (WPI), MEXT, Japan.Conflicts of Interest: The author declares no conflicts of interest.https://www.mdpi.com/article/10.3390/molecules30081749/s1https://www.mdpi.com/article/10.3390/molecules30081749/s1Molecules 2025, 30, 1749 14 of 16References1. Mitchell, R.H. Perovskites: Modern and Ancient; Almaz Press: Thunder Bay, ON, Canada, 2002.2. Abakumov, A.M.; Tsirlin, A.A.; Antipov, E.V. Transition-metal perovskites. In Comprehensive Inorganic Chemistry II (Second Edition):From Elements to Applications; Reedijk, J., Poeppelmeier, K.R., Eds.; Elsevier: Amsterdam, The Netherlands, 2013; Volume 2,pp. 1–40.3. Knapp, M.C.; Woodward, P.M. A-site cation ordering in AA′BB′O6 perovskites. J. Solid State Chem. 2006, 179, 1076–1085.[CrossRef]4. King, G.; Woodward, P.M. 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MDPI and/or the editor(s) disclaim responsibility for any injury topeople or property resulting from any ideas, methods, instructions or products referred to in the content.https://doi.org/10.1103/PhysRevB.97.195111https://doi.org/10.1126/science.aay7356https://doi.org/10.1039/D1TC02344Fhttps://doi.org/10.1016/j.jssc.2006.05.002https://doi.org/10.1016/j.jssc.2007.01.020https://doi.org/10.1021/acs.inorgchem.7b01042https://doi.org/10.1063/1.4882642https://doi.org/10.1063/1.4821516https://doi.org/10.1021/ic502138vhttps://www.ncbi.nlm.nih.gov/pubmed/25334034https://doi.org/10.1063/1.3369444https://doi.org/10.1134/S0036023617010089https://doi.org/10.1016/j.jallcom.2019.04.128https://doi.org/10.1107/S0108768190011041https://doi.org/10.1021/ic025980yhttps://www.ncbi.nlm.nih.gov/pubmed/12513085https://doi.org/10.1107/S0567739476001551https://doi.org/10.1016/0038-1098(75)90411-1https://doi.org/10.1063/1.4999454https://doi.org/10.1107/S1600577520001599https://doi.org/10.4028/www.scientific.net/MSF.321-324.198 Introduction  Results and Discussion  Experimental  Conclusions  References