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[Yasuo Ebina](https://orcid.org/0000-0003-3471-9825), [Yuichi Michiue](https://orcid.org/0000-0001-7185-8491), [Nobuyuki Sakai](https://orcid.org/0000-0002-9395-6751), [Takayoshi Sasaki](https://orcid.org/0000-0002-2872-0427)

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[Synthesis of Mn-bearing layered perovskite-type niobate and its delaminated nanosheet](https://mdr.nims.go.jp/datasets/fedde7ef-cd1b-4c00-8c59-133eb683f561)

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Synthesis of Mn-bearing layered perovskite-type niobate and its delaminated nanosheetDaltonTransactionsPAPERCite this: Dalton Trans., 2026, 55,5217Received 19th January 2026,Accepted 5th March 2026DOI: 10.1039/d6dt00131arsc.li/daltonSynthesis of Mn-bearing layered perovskite-typeniobate and its delaminated nanosheetYasuo Ebina, * Yuichi Michiue, Nobuyuki Sakai and Takayoshi SasakiLayered perovskite-type compounds with the general formula MCa2MnNb3TiO13 (M = K, Rb), in whichMn2+ is incorporated into the A-site of the perovskite layers, were synthesized via a unique conventionalsolid-state reaction. The synthesis was conducted by thoroughly mixing a layered perovskite precursor,MCa2Nb3O10, with ilmenite-type MnTiO3 in a stoichiometric molar ratio, followed by high-temperaturecalcination at 1373 K. Compositional and structural characterizations involving elemental analysis andRietveld refinement confirmed that the perovskite slabs in the host layers are four [Nb,Ti]O6 octahedrathick, with Ca2+ and Mn2+ ions occupying the A-sites. Ion exchange treatment with an acid solutioneffectively replaced the interlayer alkali metal ions (K+ or Rb+) with protons. Subsequent exfoliation byshaking in an aqueous tetrabutylammonium hydroxide solution yielded a light brown suspension. Thecolloidal material dispersed was deposited onto a Si substrate surface. Atomic force microscopy (AFM)revealed the presence of numerous micrometer-sized 2D nanosheets with a uniform thickness ofapproximately 2.0 nm, indicating complete exfoliation into single perovskite layers. Further in-depth ana-lysis via in-plane and out-of-plane X-ray diffraction (XRD), as well as X-ray photoelectron spectroscopy(XPS), confirmed that the obtained 2D materials correspond to individual perovskite layers derived fromthe Mn-substituted parent phase.1 IntroductionA class of compounds known as layered perovskite oxides hasgarnered significant attention owing to a wide range of func-tional properties such as dielectricity, ferroelectricity, andphotocatalytic activity based on their diverse compositionsand structures.1–5 Among them, compounds with the generalformula MAn−1BnO3n+1 (where M denotes alkali metals such asK, Rb, or Cs; A represents alkaline earth metals such as Ca orSr; and B corresponds to transition metals such as Ti, Nb, orTa) are classified as Dion–Jacobson-type layered perovskites.6–9A representative member of this series is KCa2Nb3O10, whichfeatures a layered structure consisting of perovskite-type slabscomposed of three corner-sharing NbO6 octahedra stackedalong the crystallographic c-axis. The interlayer region is occu-pied by alkali metal cations, which compensate for the nega-tive charge of the perovskite layers. These interlayer cations arereadily exchangeable under ambient conditions, enabling theintercalation of various organic molecules or metal complexesto form hybrid nanocomposites.10–15 Furthermore, this ion-exchangeability allows for the exfoliation of the layered struc-ture into unilamellar 2D nanosheets, which has been an activearea of research in recent decades.16–19 A series of related com-pounds with homologous structures, in which the thickness ofthe perovskite slabs varies with the number of NbO6 octahe-dra, has also been reported.7,16,20,21 These compounds are gen-erally represented by the formula KCa2Nan−3NbnO3n+1, where nindicates the number of octahedral layers in the perovskiteslab. Phases with n = 3 or 4 can be synthesized via convention-al solid-state reactions involving stoichiometric mixing of pre-cursor oxides followed by high-temperature calcination (typi-cally in the range of 1273–1473 K). However, such conventionalmethods are generally ineffective for synthesizing higher-orderphases with n ≥ 5. Alternatively, these homologous phasescan be obtained through a stepwise reaction approach. Forexample, heating a 1 : 1 molar mixture of KCa2Nb3O10 andNaNbO3 results in the formation of an n = 4 phase, in whichone additional NbO6 octahedral layer is incorporated into theoriginal perovskite framework, as described in the eqn (1).KCa2Nb3O10 þ NaNbO3 ! KCa2NaNb4O13 ð1ÞSimilarly, by adjusting the molar ratio of NaNbO3 to 2, 3, or4 during thermal treatment, a series of homologous layeredoxides with n = 3–7 was successfully synthesized. Owing to thefact that the thickness of the perovskite layers in these com-pounds can be precisely tuned in increments of approximately0.4 nm—corresponding to the height of a single NbO6 octa-hedron—this system has been extensively studied as a modelResearch Center for Materials Nanoarchitectonics (MANA), National Institute forMaterials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.E-mail: ebina.yasuo@nims.go.jpThis journal is © The Royal Society of Chemistry 2026 Dalton Trans., 2026, 55, 5217–5223 | 5217Open Access Article. Published on 09 March 2026. Downloaded on 3/31/2026 10:56:07 PM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article OnlineView Journal  | View Issuehttp://rsc.li/daltonhttp://orcid.org/0000-0003-3471-9825http://orcid.org/0000-0001-7185-8491http://orcid.org/0000-0002-9395-6751http://orcid.org/0000-0002-2872-0427http://crossmark.crossref.org/dialog/?doi=10.1039/d6dt00131a&domain=pdf&date_stamp=2026-03-25http://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d6dt00131ahttps://pubs.rsc.org/en/journals/journal/DThttps://pubs.rsc.org/en/journals/journal/DT?issueid=DT055013platform for investigating structure-property relationships inlayered perovskite oxides. We exfoliated the compounds with n= 3 to 6 into single-layer nanosheets and investigated theirdielectric properties. As a result, we observed a stepwiseincrease in the relative dielectric constant from ∼200 to ∼450with increasing, indicating that these nanosheets exhibit excel-lent dielectric performance despite their nanometer-scalethickness.20,22 Furthermore, as indicated in the eqn (2a) and(2b), analogous layered structures can be obtained by employ-ing other perovskite-type oxides, such as CaTiO3 or SrTiO3,demonstrating the versatility of this synthetic approach.8KCa2Nb3O10 þ CaTiO3 ! KCa3Nb3TiO13 ð2aÞKSr2Nb3O10 þ SrTiO3 ! KSr3Nb3TiO13 ð2bÞIn a manner analogous to the previously reported approach,homologous phases with the general formulaKCan−1Nb3Tin−3O3n+1 (n = 4, 5) can be synthesized by tuningthe molar ratio of CaTiO3 in the reaction mixture. In thesecases, Ca or Sr ions are incorporated into the A-site of the per-ovskite layers in place of Na ions as in the eqn (1), while Ti isco-substituted with Nb at the B-site. These results indicatethat, although the thermodynamic stability of such homolo-gous layered perovskites generally decreases with increasingslab thickness – making their synthesis via conventional solid-state methods more difficult – the reactions represented byeqn (1) and (2) enable the formation of higher-order membersin the homologous series. This is likely facilitated by thelayered perovskite matrix serving as a structural template,allowing for the controlled insertion of additional NbO6 orTiO6 octahedra and thereby incrementally increasing the per-ovskite slab thickness on a layer-by-layer basis. This templatingeffect may provide a route to access novel layered perovskitecompounds with unique compositions and architectures thatare otherwise unattainable by conventional synthetic methods.In the present study, we explored whether the synthetic strat-egy described by eqn (1) and (2) could be extended to ilmenite-type MnTiO3. While layered perovskite oxides exhibit consider-able diversity in composition and structure, their A-sites arepredominantly occupied by alkali or alkaline earth metal ions.The successful integration of such transition metals into thelayered perovskite framework would significantly broaden thefunctional landscape of these materials, particularly withrespect to their magnetic and redox-related properties.2 Experimental2.1 Reagents and materialsChemicals—K2CO3, Rb2CO3, CaCO3, Nb2O5, TiO2, and MnO(all ≥99.9% purity, supplied by Rare Metallic Co.)—were usedfor the synthesis. All other chemicals used in this study wereof analytical grade or higher. Ultrapure water (Milli-Q, resis-tivity >18 MΩ cm) was used throughout all experimental pro-cedures. The layered perovskite compounds KCa2Nb3O10 andRbCa2Nb3O10, serving as the basic frameworks, were syn-thesized by mixing K2CO3 or Rb2CO3, CaCO3, and Nb2O5 in amolar ratio of 1.1 : 4 : 3, followed by calcination at 1473 K for10 h in a platinum crucible.6,21 The ilmenite-type oxideMnTiO3 was prepared by calcining a stoichiometric mixture ofMnO and TiO2 at 1473 K for 12 h.23 The target compounds,KCa2MnNb3TiO13 and RbCa2MnNb3TiO13, were synthesized bysolid-state reaction between KCa2Nb3O10 or RbCa2Nb3O10 andMnTiO3 in a 1 : 1 molar ratio, followed by two successive calci-nation steps at 1373 K for 96 h each. To exchange the interlayerK+ or Rb+ ions with protons, 5 g of the resulting product wasstirred in 200 cm3 of 5 M HNO3 aqueous solution for 72 h.2.2 ExfoliationTo achieve exfoliation into individual nanosheets, 0.4 g of theacid-treated layered compound HCa2MnNb3TiO13·1.5H2O wasdispersed in 100 cm3 of an aqueous tetrabutylammoniumhydroxide (TBAOH) solution and agitated using a mechanicalshaker at 170 rpm for 7 days. The concentration of TBAOH wasadjusted to be stoichiometrically equivalent to the amount ofexchangeable protons in HCa2MnNb3TiO13·1.5H2O.2.3 Film fabricationTo characterize the obtained nanosheets by atomic forcemicroscopy (AFM) and in-plane/out of plane X-ray diffraction(XRD), the nanosheets were deposited onto Si substrates usingthe Langmuir–Blodgett (LB) technique. Prior to deposition,the Si substrates were cleaned by immersion in a HCl/CH3OH(1 : 1 v/v) solution for 30 min, rinsed thoroughly with Milli-Qwater, immersed in concentrated H2SO4 for another 30 min,and finally washed again with Milli-Q water. A 10 cm3 aliquotof the nanosheet suspension was centrifuged at 1500 rpm for10 min to remove unexfoliated aggregates. The supernatant(5 cm3) was then diluted with water to a final volume of250 cm3. This diluted suspension was spread onto the watersurface in a LB trough, and a monolayer film of nanosheetswas transferred onto the substrate at a surface pressure of10 mN m−1 with a lifting speed of 0.0167 mm s−1.2.4 CharacterizationsPowder XRD measurements were carried out using a RigakuUltima IV diffractometer equipped with graphite monochro-matized Cu Kα radiation source (λ = 0.15405 nm), and a scintil-lation counter. Crystal structure was analyzed by Rietveldrefinement with the program JANA2006.24 AFM observationswere performed using an AFM5000II (Hitachi High-TechCorp.). In-plane XRD and X-ray absorption near edge structure(XANES) measurements were conducted at beamline BL-6C ofthe High Energy Accelerator Research Organization (KEK) syn-chrotron radiation facility. XANES spectra were acquired intransmission mode using pelletized samples prepared bymixing each powder sample with hexagonal boron nitride(h-BN). X-ray photoelectron spectroscopy (XPS) measurementswere performed using a PHI Quantes system (ULVAC-PHI). Thesamples for XPS measurements were prepared by drop-castinga diluted nanosheet suspension onto Si substrates, allowingthem to stand for 10 min, removing the excess liquid, andPaper Dalton Transactions5218 | Dalton Trans., 2026, 55, 5217–5223 This journal is © The Royal Society of Chemistry 2026Open Access Article. Published on 09 March 2026. Downloaded on 3/31/2026 10:56:07 PM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d6dt00131adrying the substrates prior to measurement. For chemical ana-lysis, a weighed amount of sample was dissolved in a mixedacid solution of concentrated H2SO4 and HF, and the resultingsolution was examined using inductively coupled plasma (ICP)atomic emission spectrophotometry (1700HVR, SeikoInstruments Inc.) and atomic absorption spectrophotometry(SpectrAA-20, Varian, Inc.). Water content was deduced fromweight loss up to 1273 K using thermogravimetric-differentialthermal analysis (TG-DTA, Rigaku TGA-8120).3 Results and discussionTo evaluate the feasibility of the synthesis route described ineqn (3a) and (3b), equimolar amounts of MnTiO3 were mixedwith polycrystalline KCa2Nb3O10 and RbCa2Nb3O10. The result-ing mixtures were subjected to two successive heat treatmentsat 1473 K for 96 h each.KCa2Nb3O10 þMnTiO3 ! KCa2MnNb3TiO13 ð3aÞRbCa2Nb3O10 þMnTiO3 ! RbCa2MnNb3TiO13 ð3bÞFig. 1 displays XRD patterns of the obtained samples. Thebasal reflection peaks indicate an interlayer spacing of approxi-mately 1.87 nm for both samples, representing an expansionof about 0.4 nm relative to the parent compounds KCa2Nb3O10and RbCa2Nb3O10 (1.48 nm; see Fig. S1). The observed expan-sion was similar to that occurred in the reactions of (1) and(2), suggesting the formation of the target phase, in which thehost perovskite layers are expanded by an additional TiO6 octa-hedral unit. Most diffraction peaks observed for theK-containing sample could be indexed to a C-centered ortho-rhombic unit cell, while those for the Rb-containing samplecorresponded to a body-centered lattice. The refined latticeparameters are summarized in Table 1. However, certainreflections were attributed to supercell structures—2 × 2 × 2for the former and 2 × 2 × 1 for the latter. Such superstructureshave been reported in various layered perovskite-typeoxides.6,25 Taking these superstructures into account, all diffr-action peaks were successfully assigned to an n = 4 member ofa homologous series, indicating that the target phase wasobtained as a single-phase product. As a control experiment,direct synthesis of the target phase was attempted using stoi-chiometric mixtures of carbonates and oxides (Rb2CO3,CaCO3, MnO, TiO2, Nb2O5). The results revealed the formationof a multiphase product containing Mn3O4, CaMnO3, andother impurities (Fig. S2). These results suggest that the syn-thetic route described in eqn (3), involving precursor phases oflower n values, is more effective for preparing the higher-ordertarget phase.Next, the obtained materials were treated with acid solu-tions to replace the interlayer K+ or Rb+ ions with protons.Fig. 2 presents XRD patterns of the acid-treated samples. Thelattice parameters of the sample derived from the K-form weredetermined to be a = 0.38374(5) nm and c = 2.0092(3) nm, indi-cating an expansion of the interlayer spacing by approximately0.13 nm. A similar XRD profile was also observed for the acidtreatment sample prepared from the Rb form (Fig. S3). Thisvariation in lattice constants is consistent with those reportedfor Dion–Jacobson-type layered perovskites such asKCa2Nb3O10, and is attributed to the intercalation of oxoniumions into the interlayer region.7 Moreover, TG-DTA revealed thepresence of approximately 1.5 mol of interlayer water performula unit (Fig. S4), which is also in good agreement withpreviously reported acid-exchanged products of KCa2Nb3O10.26Table 2 summarizes the results of elemental analysis beforeand after the proton exchange process.For the as-synthesized samples, the elemental molar ratios,normalized to Nb = 3, were approximately (K orRb) : Ca : Mn : Nb : Ti = 1 : 2 : 1 : 3 : 1 for both the K- and Rb-con-taining compositions, which is consistent with the nominaltarget stoichiometry. In contrast, after acid treatment, theFig. 1 Powder XRD patterns of (a) KCa2MnNb3TiO13 and (b)RbCa2MnNb3TiO13.Table 1 Lattice parameters of layered perovskiteNominal composition a/nm b/nm c/nmKCa2MnNb3TiO13(Fundamental) 0.39309(9)a 0.38415(8)a 3.7311(6)(Superlattice) 0.7872(1)a 0.7684(1)a 3.7306(4)RbCa2MnNb3TiO13(Fundamental) 0.3828(1)a — 1.8658(6)(Superlattice) 0.7657(3)a — 1.8659(7)KCa2Nb3O10 3.8799(8) 0.7719(1) 2.9547(5)a The upper column lists the lattice constants for the fundamentallattice, while the lower column indicates the lattice parameters basedon the superlattice structures, if any.Dalton Transactions PaperThis journal is © The Royal Society of Chemistry 2026 Dalton Trans., 2026, 55, 5217–5223 | 5219Open Access Article. Published on 09 March 2026. Downloaded on 3/31/2026 10:56:07 PM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d6dt00131aelemental ratios of Ca, Mn, Nb, and Ti in the Rb-containingsample remained largely unchanged, whereas Rb becamenearly undetectable, indicating that Rb+ ions were almost com-pletely exchanged with oxonium (H3O+) ions. On the otherhand, in the K-containing sample, approximately 30% of theinitial K+ ions remained after the proton-exchange treatment,and the contents of Ca and Mn were lower than the ideal stoi-chiometry. This behavior has also been observed in the syn-thesis of compounds such as KCa2NaNb4O13, described by eqn(1), and is understood as a result of partial incorporation of K+ions into the A-sites of the perovskite layers during solid-statesynthesis. The excess Ca2+ and Mn2+ ions may then be accom-modated in the interlayer region, and involve the protonexchange. In contrast, due to the larger ionic radius of Rb+,such incorporation into the A-sites was not the case, whichleads to a composition closer to the ideal layered perovskitestructure in the Rb-containing sample. XANES measurementswere performed on both the K-form and H-form samples.Comparison with reference Mn oxides confirmed that Mnremains in the divalent oxidation state throughout the solid-state synthesis and subsequent the proton-exchange processes(Fig. S5). This result is consistent with charge balance basedon the nominal composition.Based on these findings, Rietveld refinement was carriedout for more quantitative structural characterization. Since theK-containing sample required a doubled unit cell along thec-axis relative to the Rb-containing sample, and consideringthe structural complexity arising from the solid solution behav-ior of K+, Ca2+, and Mn2+ occupying both the interlayer andA-sites in the perovskite framework, structure refinement wasperformed on the Rb-containing sample, which is expected tohave a simpler and more ordered structure. Specifically, super-structure features suggested by lattice parameter analysis weredisregarded, and instead a model based on a fundamentallayered perovskite framework was adopted, referring to pre-viously reported structurally similar compounds.27 Refinedoccupancies and atomic displacement parameters may beaffected by this simplification of the subcell model, but arereliable enough to discuss the basic feature of the structure. Inthis model, Ca2+ and Mn2+ occupy the A-sites within the hostperovskite layers at a molar ratio of 2 : 1 as a whole, while Nb5+and Ti4+ occupy the B-sites at a molar ratio of 3 : 1. As shownin Fig. 3 and Table 3, satisfactory refinement results wereobtained, confirming the successful synthesis of the targetedlayered perovskite structure with Mn2+ incorporated into theA-sites. In this refinement, fitting was performed with MnTiO3included as an impurity phase. Its refined with a phase frac-tion of 3.3%, indicates the almost full reaction of MnTiO3according to eqn (3b). Although the initial structural modelassumed a solid solution of Nb5+ and Ti4+ with a molar ratio of3 : 1, the refinement process revealed a pronounced redistribu-tion of Nb5+ ions. Specifically, Nb5+ progressively accumulatedat the B-site positions located closer to the surface of the per-ovskite layer, ultimately resulting in 100% occupation of thesesites by Nb5+ (denoted as Nb(2)). In contrast, the B-sites situ-ated nearer to the center of the perovskite layer (Nb(1), Ti(1))converged to a mixed-occupancy configuration in which Nb5+and Ti4+ form a solid solution. This site preference is plausiblyattributed to electrostatic considerations based on Pauling’sprinciple.28 In the present perovskite-related structure, theA-sites within the perovskite layer are occupied by divalentCa2+/Mn2+ cations, while the interlayer region is filled withmonovalent Rb+ cations. Consequently, Nb5+ cations areexpected to preferentially occupy B-sites adjacent to the inter-layer region to stabilize the local charge balance, leading toFig. 2 Powder XRD pattern of the acid-treated product fromKCa2MnNb3TiO13.Table 2 Elemental analysis results and molar ratios of each layered perovskiteNominal composition K or Rb Mn Ca Nb TiKCa2MnNb3TiO13 6.7 (1.00) 10.5 (1.03) 15.7 (1.95) 57.2 (3.00) 10.8 (0.95)Acid-exchanged product from K-form 3.3 (0.31) 9.6 (0.89) 16.5 (1.93) 60.7 (3.00) 11.1 (0.91)RbCa2MnNb3TiO13 12.3 (0.99) 10.0 (1.06) 15.0 (2.02) 52.8 (3.00) 10.3 (0.97)Acid-exchanged product from Rb-form 0.6 (0.04) 10.9 (1.02) 16.8 (1.99) 60.1 (3.00) 11.6 (0.96)The values are given in wt%. The values in parentheses represent the molar ratios normalized with Nb = 3.00.Paper Dalton Transactions5220 | Dalton Trans., 2026, 55, 5217–5223 This journal is © The Royal Society of Chemistry 2026Open Access Article. Published on 09 March 2026. Downloaded on 3/31/2026 10:56:07 PM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d6dt00131athe observed enrichment of Nb5+ near the perovskite layersurface.Subsequently, we examined the exfoliation of the preparedlayered perovskite into unilamellar nanosheet. When the acid-treated product derived from the Rb-form,HCa2MnNb3TiO13·1.5H2O, was vigorously agitated with anaqueous TBAOH solution, the mixture transformed into a lightbrown colloidal suspension (Fig. S6). The colloidally dispersedsample was deposited onto a Si substrate via the LB techniqueand subsequently examined by AFM (Fig. 4). The AFM imagesrevealed a large number of rectangular, ultrathin, sheet-likestructures. The image provides further evidence for uniformand unilamellar nature of the nanosheet. The height profilehistogram (Fig. 4c) exhibited two distinct peaks: one corres-ponding to the height of the Si substrate and the other to thatof the nanosheets, indicating a uniform thickness for the exfo-liated perovskite layers. The nanosheet thickness was esti-mated to be approximately 2.0 nm. This value is in close agree-ment with the theoretical thickness of 1.859 nm, calculatedfrom the outermost O–O distance in a single perovskite layeras determined by Rietveld refinement, thereby confirming suc-cessful exfoliation into individual monolayers. The slightlylarger experimental thickness compared to the calculatedvalue is commonly observed in various nanosheet systems andis attributed to the presence of surface-adsorbed watermolecules.29–32To examine the crystal structure, in-plane XRD measure-ments were performed on the monolayer film ofCa2MnNb3TiO13 nanosheets deposited on the substrate. Asshown in Fig. 5, sharp diffraction peaks indicative of high crys-tallinity were observed, and these peaks could be indexed to a2D square lattice with a lattice parameter of a = 0.38372(4) nm.This result clearly demonstrates that the fundamental perovs-kite lattice is preserved after exfoliation into nanosheets.The out-of-plane XRD pattern was measured in the Bragg–Brentano geometry using a powder X-ray diffractometer (Fig. 6)and exhibited characteristic oscillatory scattering features. Thecontinuous nature of the diffraction profile suggests theabsence of repeating periodicity along the thickness (c-axis)direction. The observed oscillations are attributed to structuralarchitecture across the nanosheet thickness. To validate thisinterpretation, the scattering intensity along the z-direction ofmonolayer perovskite nanosheets was calculated based on theFig. 3 Structure refinement of X-ray powder diffraction data for RbCa2MnNb3TiO13. Blue: observed, red: calculated, green: Bragg reflections, black:the difference.Table 3 Structural parameters from crystal structure refinement forRbCa2MnNb3TiO13 in space group P4/mmm (123)x y z Occ. U SiteNb(1) 0 0 0.10461(13) 0.5 0.0037(7) 2Nb(2) 0 0 0.32929(10) 1.0 0.0149(7) 2Ti(1) 0 0 0.10461(13) 0.5 0.0037(7) 2Ca(1) 0.5 0.5 0 0.89(6) 0.034(3) 1Ca(2) 0.5 0.5 0.2207(2) 0.56(3) 0.046(2) 2Mn(1) 0.5 0.5 0 0.11(6) 0.034(3) 1Mn(2) 0.5 0.5 0.2207(2) 0.44(3) 0.046(2) 2Rb(1) 0.5 0.5 0.5 1.0 0.0505(16) 1O(1) 0 0 0 1.0 0.076(2) 1O(2) 0 0.5 0.1034(8) 1.0 0.076(2) 4O(3) 0 0 0.1977(8) 1.0 0.076(2) 2O(4) 0.5 0 0.3051(6) 1.0 0.076(2) 4O(5) 0 0 0.4136(10) 1.0 0.076(2) 2a = 0.3837 nm, c = 1.872 nm, V = 0.27557(1) nm3, Rp = 8.03%, Rwp =11.04%, Re = 4.54%, S = 2.43.Fig. 4 AFM observation data of Ca2MnNb3TiO13 nanosheets depositedon a Si substrate. (a) and (b) topographic image and (c) height histogram.Dalton Transactions PaperThis journal is © The Royal Society of Chemistry 2026 Dalton Trans., 2026, 55, 5217–5223 | 5221Open Access Article. Published on 09 March 2026. Downloaded on 3/31/2026 10:56:07 PM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d6dt00131aatomic coordinates obtained from the aforementionedRietveld refinement, according to the eqn (4) and (5)below.21,33 The resulting simulated profile closely reproducedthe experimental profile.F00l ¼Xjfj e2πið2zj sin θf =λÞ ð4ÞI00l ¼ 1þ cos2 θsin2 θ cos θF00lF*00l ð5ÞHere, F00l and I00l denote the structure factor and the scatter-ing intensity of a single-layer perovskite nanosheet along the00l direction, respectively; fj and zj denote the atomic scatter-ing factor and the z-coordinate of the j-th atom. θ is the diffrac-tion angle and λ is the X-ray wavelength (Cu Kα, λ =0.15405 nm). This agreement supports the conclusion that theperovskite layer is composed of four corner-sharing [Nb,Ti]O6octahedra, indicating that the perovskite framework is retainedalong the layer normal.Fig. 7 shows the wide-scan XPS spectrum ofCa2MnNb3TiO13 nanosheets obtained from the Rb-containingprecursor (Fig. S7). The elemental composition of eachnanosheet, determined from the integrated peak areas andnormalized to Nb = 3.00, is summarized in Table 4.XPS analysis detected Mn signals in nanosheets derivedfrom both K- and Rb-containing layered perovskites. Thenanosheets obtained from the Rb-based precursors exhibitedno detectable Rb signal, and the elemental ratios of Ca, Nb, Ti,and Mn were consistent with those determined by elementalanalysis after ion exchange. This confirms that the perovskitelayer framework was preserved during the exfoliation process.In contrast, nanosheets derived from the K-containingsamples exhibited residual K signals and a lower Mn content.These findings are in agreement with the post-ion-exchangeelemental analysis, suggesting that a fraction of the K ions isincorporated into the perovskite layers and remains even afteracid treatment and delamination.4 ConclusionsA new class of layered perovskite oxides, KCa2MnNb3TiO13 andRbCa2MnNb3TiO13, was successfully synthesized by calciningthe precursors KCa2Nb3O10 or RbCa2Nb3O10 with illmenite-type MnTiO3. Compositional and structural characterizationsconfirmed that these compounds belong to the Dion–Jacobsonseries of layered perovskites. The original three-layer perovskiteslabs composed of corner-sharing NbO6 octahedra wereexpanded through the incorporation of MnTiO3, forming anovel four-layer perovskite structure comprising mixed [Nb,Ti]O6 octahedra. To the best of our knowledge, there have beenno prior reports of Dion–Jacobson type layered perovskiteFig. 5 In-plane XRD pattern of a monolayer film of Ca2MnNb3TiO13nanosheets deposited on a Si substrate using the LB method.Fig. 6 Out-of-plane XRD pattern of Ca2MnNb3TiO13 nanosheetsmonolayer on a Si substrate using the LB method. Red: observed, cyan:calculated. The part indicated by the arrow corresponds to the humprelating to the Si substrate.Fig. 7 X-ray photoelectron spectroscopy of Ca2MnNb3TiO13nanosheet.Table 4 Elemental ratios of each Ca2MnNb3TiO13 nanosheet estimatedfrom XPSK Rb Ca Mn Nb TiFrom K-form 0.05 — 2.15 0.88 3.00 1.17From Rb-form — 0.00 2.03 1.11 3.00 1.10Paper Dalton Transactions5222 | Dalton Trans., 2026, 55, 5217–5223 This journal is © The Royal Society of Chemistry 2026Open Access Article. Published on 09 March 2026. Downloaded on 3/31/2026 10:56:07 PM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d6dt00131aoxides containing Mn ions at the A-site, and the syntheticroute developed in this study offers a promising strategy toexpand the compositional diversity of layered perovskites.Furthermore, proton exchange followed by exfoliation enabledthe isolation of perovskite nanosheets with a thickness corres-ponding to four octahedral layers, while retaining the originalperovskite framework. The preservation of the perovskite archi-tecture in the exfoliated nanosheets was verified by AFM, in-plane and out-of-plane XRD, and XPS analyses. These findingsdemonstrate that the present synthetic approach is an effectivestrategy for the rational design of functional layered perovskiteoxides and their corresponding nanosheet derivatives.Conflicts of interestThere are no conflicts to declare.Data availabilityAll data supporting this study are available within the articleand its supplementary information (SI). Supplementary infor-mation is available. See DOI: https://doi.org/10.1039/d6dt00131a.AcknowledgementsThis work was supported by World Premier InternationalResearch Center Initiative (WPI), Ministry of Education,Culture, Sports, Science and Technology (MEXT), Japan, andCREST of the Japan Science and Technology Agency (JST)(grant no. JPMJCR22B1), Japan. The in-plane XRD measure-ments were performed under the approval of the PhotonFactory Program Advisory Committee (Proposal No.2024G501). This work was supported by “Advanced ResearchInfrastructure for Materials and Nanotechnology in Japan(ARIM)” of the MEXT. 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