# Fileset [PCVO manuscript-author-update-100826.docx](https://mdr.nims.go.jp/filesets/021d6851-676d-4024-bd8c-52cce982e2db/download) ## Creator Ruifeng Tian, [Jie Chen](https://orcid.org/0000-0001-9609-669X), Zhiyan Shao, Feng Wu, Jiayi Guan, Wei Wu, Wanli He, Yuanzhe Li, Yuemei Li, Jin-Ming Chen, Zhiwei Hu, Pengda Ye, Yuxiang Chen, Jiayi Han, Hua Zhang, Baoshan Song, [Alexei A. Belik](https://orcid.org/0000-0001-9031-2355), Yanfeng Guo, Meiling Jin, Jiabin Qiao, Fan Yang, Xiang Li ## Rights ©2026 American Physical Society[In Copyright](http://rightsstatements.org/vocab/InC/1.0/) ## Other metadata [Mass enhancement and lone-pair-driven structural distortion in PbC u 3 V 4 O 12 ](https://mdr.nims.go.jp/datasets/52c43d62-d2e3-4447-9644-c75e058fd58d) ## Fulltext Mass Enhancement and Lone-Pair-Driven Structural Distortion in PbCu3V4O12Ruifeng Tian1, Jie Chen1*, Zhiyan Shao1*, Feng Wu1,2, Jiayi Guan1,3, Wei Wu2, Wanli He1, Yuanzhe Li1, Yuemei Li1, Jin-Ming Chen4, Zhiwei Hu5, Pengda Ye1,6, Yuxiang Chen1, Hua Zhang2, Baoshan Song1, Alexei A. Belik7, Yanfeng Guo8, Meiling Jin1*, Jiabin Qiao1*, Fan Yang1, and Xiang Li1*1Key Lab of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) and School of Physics, Beijing Institute of Technology, Beijing 100081, P. R. China2Institute of physics, Chinese Academy of Sciences, Beijing 100091, P. R. China3Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai 201203, P. R. China4Department of Electrophysics, National Yang Ming Chiao Tung University (NYCU), Hsinchu 300, Taiwan5Max-Planck-Institute for Chemical Physics of Solids, Dresden 01187, Germany6Key Laboratory of Biomimetic Robots and Systems, Ministry of Education, State Key Laboratory of Intelligent Control and Decision of Complex System, and School of Mechatronical Engineering, Beijing Institute of Technology, Beijing 100081, China.7Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan8State Key Laboratory of Quantum Functional Materials, School of Physical Science and Technology and ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China1 AbstractA-site-ordered perovskites (AA’3B4O12) provide a structurally robust platform for exploring correlated-electron behavior, offering unusual opportunities to disentangle the roles of orbital degree of freedom, bonding interaction, and local structural distortions. In this work, we synthesize a new A-site-ordered perovskite PbCu3V4O12 under high-pressure and high-temperature conditions and perform comprehensive structural and physical characterizations. PbCu3V4O12 crystallizes in the cubic Im-3 structure, yet its structural parameters deviate markedly from the established ionic-radius trend in the ACu3V4O12 (A = Mn, Cu, Ca) series. This deviation reveals local structural modifications driven by the Pb2+ lone-pair electrons. The compound exhibits metallic behavior down to at least 8 K and shows a moderately enhanced Sommerfeld coefficient, with density-functional calculations confirming the associated mass enhancement. Comparison of the experimental and theoretical magnetic susceptibilities further indicates an additional contribution from Stoner mechanism. These results identify PbCu3V4O12 as a rare example of a 3d-electron metallic vanadate with moderate electronic correlations, demonstrating how A-site chemistry and lone-pair-induced local distortions can be used to engineer correlated electronic states in perovskite-related materials.1. IntroductionThe exploration of perovskite-type oxides (ABO3) continues to draw considerable interest due to the broad range of physical phenomena they host. Achieving wider tunability of electronic and magnetic properties, or improving functional performance, requires the discovery of new compounds and strategies for systematic materials design. One route involves replacing the B-site cation with different transition metal ions arranged in ordered configurations, forming double or triple perovskites [1,2]. Another route is to introduce cation ordering at the A-site, giving rise to the A-site-ordered perovskite family. In the AA’3B4O12 structure, the A’-site is typically occupied by smaller cations such as Cu2+ or Mn2+, while the A-site accommodates alkali, alkaline-earth, or transition-metal ions [3,4].Substitution at either the A- or B- site in AA’3B4O12 provides an effective means to tune a wide range of physical properties. Reported transport behavior ranges from metallic to semiconducting or insulating, including metal-insulator transitions such as that observed in CaCu3Fe4O12 [5]. The magnetic properties likewise vary, spanning paramagnetic, antiferromagnetic, ferrimagnetic, and ferromagnetic regimes [6-8]. Despite this diversity, most members retain a robust cubic Im-3 structure that is largely insensitive to specific A- or B-site chemistries, in clear contrast with simple or double perovskite. This structural stability offers a rare platform for disentangling the roles of orbitals degrees of freedom, bonding interactions, and subtle local distortions in determining the macroscopic physical properties.The metallic compound CaCu3Ru4O12 is one of the most extensively studied A-site-ordered perovskite owing to its Kondo-like behavior and heavy-fermion characteristics. The origin of its mass enhancement remains under debate [9-12]. Notably, its Sommerfeld coefficient (γ) is enhanced by a factor of 20- 30 relative to conventional metals, an unusual feature for systems without 4f electrons [13]. Similar enhanced γ value has been reported across several A-site-ordered perovskites, including ACu3Ru4O12 (A = Na, La), ACu3Ir4O12 (A = Ca, La), ACu3V4O12 (A = Mn, Cu), and CaCu3Co4O12, with γ values spanning 75- 336 mJ/(mol K2) [5,9,13-25]. The widespread enhancement underscores the importance of the unique A-site-ordered crystal structure in governing the correlated-electron behavior of this family.In this study, we synthesized a new A-site-ordered perovskite, PbCu3V4O12, under high-pressure and high-temperature conditions and carried out detailed structural and physical characterizations. PbCu3V4O12 preserves the cubic Im-3 (No. 204) symmetry typical of this class, yet its lattice parameter, bond lengths, and bond angles deviate markedly from the trends established in ACu3V4O12 (A = Cu, Mn, Ca) when plotted against A-site ionic radius. This deviation indicates local structural modifications introduced by Pb2+, highlighting the influence of the Pb2+ lone-pair electrons on subtle local distortions. PbCu3V4O12 exhibits metallic conductivity down to at least 8 K and shows an enhanced Sommerfeld coefficient, with density-functional (DFT) calculations confirming a corresponding mass enhancement. Moreover, comparison between experimental magnetic susceptibility and theoretical estimates suggests an additional contribution from the Stoner mechanism.Finally, we summarize and compare the structural and physical properties of reported metallic A-site-ordered perovskites to place PbCu3V4O12 within the broader context of this compound family. These insights provide guidance for future materials design based on A-site ordering and lone-pair-induced local structural modifications.2. ExperimentalSynthesis: Polycrystalline PbCu3V4O12 was synthesized under a high-pressure condition by solid- state reaction from powders of PbO (99.999%, Aladdin, Shanghai, China), CuO (99.9%, Aladdin, Shanghai, China), VO2 (99.99%, Aladdin, Shanghai, China). Initial synthesis of PbCu3V4O12 using a starting molar ratio of PbO: CuO: VO2 = 1:3:4 resulted in the presence of a PbVO3 impurity phase. Systematic optimization of the starting composition showed that a molar ratio of PbO: CuO: VO2 = 1: 3.75: 4.75 yields the lowest impurity level (Figure S1 [26]). This optimized ratio was used for the preparation of all samples investigated in this study. PbCu3V4O12 was synthesized at 10 GPa and 850℃ with a Walker-type multi-anvil high-pressure apparatus (LPR-1000, Max Voggenreiter Germany). The samples were kept at the target pressure and temperature for 30 minutes during high-pressure synthesis, then quenched to room temperature before the pressure was released.Crystal Structure Determination: Polycrystalline samples obtained from high-pressure synthesis were characterized by laboratory X-ray diffraction (XRD) using a Bruker D2 Phaser diffractometer with Cu Kα radiation, as well as by synchrotron XRD at beamline BL02B2 at SPring-8 (λ = 0.41306 Å). Rietveld refinements were performed using the RIETAN-FP and VESTA software [27,28].Valence State Determination: Cu K-edge X-ray absorption spectroscopy (XAS) measurements were performed at beamline BL17B1 of the Shanghai Synchrotron Radiation Facility. Pb L3-edge XAS data were obtained at beamline BL12B2 of SPring-8, Japan.Grain size Determination: Morphological characterization of the pristine polycrystalline sample was performed using a Jeol JSM-IT700HR scanning electron microscope (SEM). Measurements of Transport Properties: The temperature dependence of electrical resistivity was measured using an Oxford TeslatronPT 14 T with a Stanford SR830 Lock-in amplifier. Resistivity was measured using the four-probe method in the van der Pauw configuration in the range 1.8 ≤ T ≤ 300 K. Owing to the moderate density and poor interparticle connectivity of the polycrystalline pellet, electron-transport measurements were challenging. The measurements were therefore performed by sealing a piece of the sample in a diamond anvil cell (DAC; culet diameter 200 µm), using platinum wires as electrical leads and NaCl as the pressure-transmitting medium. The DAC was used to hold the sample. As confirmed by ruby fluorescence measurements, the pressure during the measurement was 0.4 GPa. The temperature dependence of specific heat and thermoelectric power was measured using a Physical Property Measurement System (PPMS, Quantum Design Inc.). Specific heat measurements were performed using Apiezon-N grease for thermal contact between a pellet of polycrystalline sample and the sample stage in the range 1.8 ≤ T_≤ 300 K.Measurements of Magnetic Properties: The field-cooling (FC) and zero-field-cooling (ZFC) of the samples were performed using a Magnetic Properties Measurement System (MPMS, Quantum Design Inc.), over the temperature range 1.8 ≤ T_≤ 300 K under an applied field of 1 kOe. The isothermal magnetization (M-H) curves were obtained by sweeping the field from -70 kOe to +70 kOe at 2, 50 and 200 K.Density Functional Theory (DFT) calculations: DFT calculations were performed using the Vienna ab inito Simulation Package (VASP). The projector augmented wave (PAW) was employed as the pseudopotentials [29-31]. The electronic correlations were considered by the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) exchange potential [32]. The plane-wave cutoff energy is . A -point grid is adopted. The onsite Coulomb interaction strength is set to be for the orbital of Cu and for the orbital of V. In the structure used for our calculations, the Pb atom was fixed at the ideal position . Magnetic ordering was not included in the calculations.3. Results and discussionFor detailed structural characterization, synchrotron XRD measurements were performed with an incident wavelength of λ = 0.41306 Å. We examined the crystal structure using an A-site-ordered perovskite model with space group Im-3 (No. 204), which has been previously reported for other A-site-ordered perovskites CaCu3B4O12, (B = Ti, V, Cr, Mn, Co, Ru, and Ir). The final refined pattern is shown in Figure S2(a) [26], yielding refinement qualities of Rwp = 7.96 % and Rp = 5.88 %, where all site occupancies were fixed to 1. The thermal displacement parameter of Pb site (Uiso = 0.00979(9) Å2) is much larger than those of Cu (Uiso = 0.00226(9) Å2) and V (Uiso = 0.00215(9) Å2) sites. This is counterintuitive because, as a heavy element, Pb is generally expected to exhibit a smaller thermal displacement than lighter elements. Such an anomalously large U may originate from static disorder, prompting a closer examination of possible A-site deficiencies. Upon refining the cation-site occupancies, the Cu and V atoms at the 6b (0, 1/2, 1/2) and 8c (1/4, 1/4, 1/4) sites were found to be nearly fully occupied, whereas the Pb occupancy at the 2a (0, 0, 0) site converges to 0.886(1). Incorporation of this Pb deficiency leads to a reduced thermal displacement of Pb (Uiso = 0.00715(7) Å2), although the value remains larger than those of Cu (Uiso = 0.00453(8) Å2) and V (Uiso = 0.00376(7) Å2). The refinement quality also improves to Rwp = 6.20 % and Rp = 4.63 %. The refined pattern is presented in Figure S2(b) [26], and the corresponding structural parameters are summarized in Table S1 [26].Figure. 1 Rietveld refinement of the synchrotron XRD profile (λ = 0.41306 Å) collected at room temperature for polycrystalline PbCu3V4O12. A cubic (Im-3) model was used in the analysis. The crosses and solid lines show the observed and calculated patterns, respectively, with their differences shown at the bottom. The expected Bragg reflections are marked by ticks for the Im-3 structure (top; 99.01 wt.%) and PbVO3 (bottom; 0.99 wt.%). The crystal structure image of the cubic PbCu3V4O12 is shown in the inset, in which octahedral VO6 and square CuO4 are drawn in yellow and blue, respectively. The Pb atom position at the A-site is drawn as a grey sphere.Unusually large Uiso values at the A-site in AA’3B4O12, have been reported for CuCu3V4O12 and MnCu3V4O12, with room-temperature values of 0.0446 and 0.0222 Å2 respectively [15,16]. Owning to the smaller ionic radii of Cu2+ and Mn2+, thermal oscillations at the A-site are considerably enhanced. These loosely bound A-site ions were shown to rattle within the oversized icosahedral cages, as demonstrated for Cu2+ and Mn2+. The rattling of Cu2+ at the A-site was further supported by heat-capacity measurements that revealed Einstein-like vibrational modes at low temperatures. Such behavior, however, has not been reported for the isostructural compound CaCu3V4O12. Considering that Pb2+ has an even larger ionic radius than Ca2+, the rattling of A-site Pb2+ is unlikely to account for the observed large thermal displacement. Therefore, another possibility involving displacive disorder was considered, in which the A-site cation may shift from the ideal 2a position to more general sites.An A-site-ordered perovskite BiMn7O12 (also written as BiMn3Mn4O12) was previously reported to crystallize in a structure featuring a Bi-site splitting model, in which the lone electron pair of Bi3+ was proposed to drive to a displacement from the ideal 2a (0, 0, 0) to the 16f (x, x, x) site with an occupancy of 0.125 [33]. Considering that Pb2+ also possesses a lone electron pair as Bi3+, a similar splitting model was examined for Pb in the present compound. Rietveld refinement was performed using the Im-3 (No. 204) structural model, where Pb was placed at the 16f (x, x, x) site with an initial occupancy of 0.125, while all other atomic positions were kept unchanged. Note that the number of atoms per formula unit (n) is calculated as n = (m × occ.)/Z, where m is the Wyckoff multiplicity, occ. is the site occupancy, and Z is the number of formula units per unit cell. The definition of occ. depends on the refinement program, the occ. values reported here follow the convention implemented in the RIETAN-FP software. Within this model, the refined displacement parameter for Pb is reduced to Uiso = 0.00630(7) Å2, compared with Uiso (Cu) = 0.00452(8) Å2 and Uiso (V) = 0.00375(7) Å2. The refined Pb position shows a clear deviation from the ideal 2a (0, 0, 0) site, yielding x = 0.040(2). The Pb-site deficiency is retained in this model, resulting in a refined chemical composition of Pb0.886Cu3V4O12. Although the Pb-site splitting model leads to a reduced Uiso value for Pb, it does not fully account for the comparatively large Pb displacement parameter. Moreover, the refinement quality is not improved, as indicated by unchanged R values.Furthermore, considering that CuCu3V4O12 can be stabilized under high-pressure and high-temperature conditions, this suggests that Cu can be accommodated at the A site of AA’3B4O12. Therefore, we examined a structure refinement based on a structure model in which the A site is simultaneously occupied by Pb and Cu atoms in a disordered manner. The refinement yields A-site occupancies of 0.823 for Pb and 0.177 for Cu, corresponding to a chemical composition of Pb0.823Cu0.177Cu3V4O12. Within this model, the displacement parameter at the A site remains slightly larger than those of the lighter-atom sites, as listed in Table 1. A comparison of the R values does not allow a definitive conclusion as to which structural model is superior. However, considering the elemental ratios of the starting materials described in the synthesis section, the refined composition of Pb0.823Cu0.177Cu3V4O12 is very close to the nominal Pb: Cu: V ratio used for synthesis. This consistency supports the validity of the A-site disorder model, in which Pb and Cu coexist at the A site, for describing the compound synthesized in this work. As described in the Experimental section, systematic optimization of the starting composition shows that a molar ratio of PbO: CuO: VO2 = 1: 3.75: 4.75 yields the lowest impurity level. A comparison of samples prepared with different starting ratios is presented in Figure S1 [26]. These results imply that there is an intrinsic tendency that prevents the A site from being fully occupied by Pb atoms.Cation-site deficiency has been widely reported in A-site-ordered perovskites, such as Ln2/3Cu3Ti4O12 (Ln = lanthanide), CaCu3Ti4O12, LaCu3Pt3.75O12, and La3Ru4O12 [34-37]. The ability to accommodate a substantial concentration of vacancies reflects the structural robustness of A-site-ordered perovskites. In the literature, (DyδMn1-δ)Mn3Mn4O12 has also been reported to exhibit a comparable degree of A-site disorder to that observed in Pb0.823Cu0.176Cu3V4O12, in which the A site is occupied by 91.1% Dy and 8.9% Mn [38]. Elucidating the physical origin of A-site disorder in Pb0.823Cu0.176Cu3V4O12 will likely require further investigation of the local chemical coordination environment, for example, by pair distribution function (PDF) analysis. Based on the high-resolution synchrotron XRD data presented in this work and a comparison of different structural models, we conclude that the A-site disorder model yielding Pb0.823Cu0.177Cu3V4O12 provides the most reasonable description of the compound synthesized under the present conditions. Moreover, consistently large displacement parameters are obtained for Pb site across the different structural models, indicating that this feature is intrinsic to the Pb atoms rather than an artifact of a particular structural model. The stereochemical activity of the Pb2+ lone pair is a plausible origin of this behavior; a similar phenomenon has also been observed in Bi-based compounds [39]. The Rietveld refinement results for A-site disorder model are shown in Figure 1 and Table 1. It is worth noting that the structural parameters including lattice parameters, bond lengths, and bond angles, obtained from the different structural models are nearly identical. These are summarized in Table S3 [26] of the Supplemental Information. For simplicity, the nominal formula PbCu3V4O12 is adopted in the following discussion.Table 1 Atomic coordinates and equivalent isotropic displacement parameters (Uiso, 10-3Å2) for a cubic PbCu3V4O12 as measured by the synchrotron X-ray diffraction at room temperature Site WP Occ. x y z Uiso Pb 2a 0.823(2) 0.0 0.0 0.0 6.68(7) Cu1 2a 0.176 0.0 0.0 0.0 6.68 Cu2 6b 1 0 0.5 0.5 4.59(8) V 8c 1 0.25 0.25 0.25 3.84(7) O 24g 1 0 0.3065(2) 0.1866(2) 4.3(3)WP: Wyckoff position. Space group: Im-3 (Cubic; No.204); lattice constants a = 7.33064(1) Å; cell volume = 393.9367(11) Å3; dcal = 6.476 g cm-3; Chemical formula sum: Pb0.823Cu0.177Cu3V4O12 (Z = 2); and the final R values are 6.20 % (Rwp), 4.63 % (Rp), 3.10 % (RB), and 1.75 % (RF).To confirm valence states, the polycrystalline sample was examined by XAS, as shown in Figure 2. The valence states of Pb and Cu were identified as 2+ by comparison with reference samples. The Pb-O, Cu-O, and V-O bond lengths obtained from Rietveld refinement are summarized in Table S3 [26]. The refined V-O bond length of 1.935 Å yields a bond-valence sum (BVS) of +3.99, supporting the tetravalent state of vanadium in PbCu3V4O12.Figure 2 The XAS spectra of PbCu3V4O12 at the (a) Cu-K edge and (b) Pb-L3 edge.The temperature dependence of resistivity ρ(T), shown in Figure 3(a), indicates that PbCu3V4O12 remains metallic down to at least 8 K. The estimated residual-resistivity ratio (RRR) between 300 K and 8 K is merely 1.27, which is comparable to those reported for proposed semimetals [40,41]. The small RRR is likely associated with the presence of the grain-boundary effect in the main phase and insulating PbVO3 impurity. The pristine sample obtained from high-pressure and high-temperature synthesis forms a moderately dense pellet, which may enhance grain-boundary scattering and result in a reduced RRR. For comparison, the estimated RRR for polycrystalline ACu3V4O12 compounds are summarized in Table 2. All vanadate compounds in this family, ACu3V4O12 (A = Na, Ca, Mn, Cu, Y, Pb), exhibit RRR values in the range of 1-2, indicating that a low RRR is a common characteristic of this compound family. Similar to PbCu3V4O12, resistivity measurements for CuCu3V4O12 have been reported to be challenging due to poor interparticle connectivity, contact resistance, or grain-boundary resistance; therefore, ρ(T) was measured using a DAC [16,42]. Such grain-boundary-dominated transport behavior is therefore likely to play an important role in determining the overall transport properties of this compound family.The magnitude and temperature dependence of the thermoelectric power (S), shown in Figure 3(b), further confirm the metallic nature of this compound. The Seebeck coefficient increases upon cooling from 300 K and begins to decrease below approximately 15 K, approaching zero at the lowest measured temperature (= 2 K). The S(T) changes sign from negative to positive upon cooling through ~40 K, which may be indicative of temperature-driven band crossing. The S(T) is highly sensitive to the asymmetry of the electronic density of states near the Fermi energy (EF) [43]. Although the electrical resistivity is less sensitive to such electronic asymmetry than the Seebeck coefficient, it may still exhibit related signatures, since resistivity depends on carrier mobility and the density of states at EF. As shown in Figure 3(a), the slope of ρ(T) exhibits a subtle change around 40 K. This feature becomes more discernible in the temperature derivative (Figure S3 [26]), where a minimum in appears near 40 K, as indicated by the dashed line. As discussed above, resistivity is inherently less sensitive to such band-structure changes than the Seebeck coefficient; therefore, only a modest variation is observed in compared with the more pronounced feature in the S(T). To further elucidate the temperature-driven band crossing, theoretical simulations beyond DFT calculations are required, as standard DFT provides the band structure at 0 K. This issue remains to be investigated in future work.Figure 3 Temperature dependence of (a) resistivity ρ(T) with ρ(T2) shown in the inset, (b) thermopower S(T), (c) thermal conductivity κ(T), and (d) an SEM image of a polished surface of pristine polycrystalline PbCu3V4O12.A slight upturn of resistivity below 8 K may originate from the small amount of PbVO3 impurity (0.99 wt. %, as obtained from Rietveld refinement). Pure PbVO3 is insulating, and its resistivity increases from ~10 cm at 300 K to 103 cm below 50 K [44]. Thus, the overall resistivity of the PbCu3V4O12 sample may contain a minor insulating contribution from PbVO3, leading to the observed upturn below 8 K. Nevertheless, the conducting behavior of PbCu3V4O12 remains robust. The resistivity of PbCu3V4O12 deviates from a T2 dependence below ~60 K, as shown in the inset of Figure 3(a), whereas CaCu3V4O12 begins to deviate from Fermi-liquid behavior below about 15 K. Downward deviations from Fermi-liquid behavior have also been reported for NaCu3V4O12 and YCu3V4O12 at low temperatures [14]. The low-temperature resistivity of PbCu3V4O12 does not exhibit a clear T2 dependence expected for a conventional Fermi liquid. This behavior is likely associated with disorder-related scattering effects. The polycrystalline PbCu3V4O12 sample forms a moderately dense pellet, in which grain-boundary scattering and intergranular effects can lead to deviations from the intrinsic Fermi-liquid-like behavior.The thermal conductivity (κ) of PbCu3V4O12, shown in Figure 3(c), exhibits glass-like behavior similar to that reported for CaCu3Ir4O12 and PbCu3Ru4O12 [24,45]. To estimate the electronic contribution, the Wiedemann-Franz law, κe = LσT (where L is Lorenz number), was applied. The calculated κe is negligible compared with the total thermal conductivity (κtotal). The average grain size of the pristine sample, revealed by the SEM image in Figure 3(d), is approximately 5- 10 µm, which is much larger than the phonon mean free path. This rules out grain-boundary scattering as the origin of the glass-like behavior. It should be noted that the surface was obtained by polishing a moderately dense pellet of the pristine sample. The relatively low density of the pellet, together with the polishing process, leads to the pores observed in the SEM image.Figure 4 (a) Temperature dependence of χ of polycrystalline PbCu3V4O12, measured in a field of 1 kOe. The dashed line is the fitting by the function of χ = χ0 (1-aT2). Isothermal magnetizations at 2, 50, and 200 K are shown in the inset. (b) Alternative plot of the χ - T data, compared with those of CaCu3V4O12 and MnCu3V4O12 [14,15].The temperature-dependence of magnetic susceptibility (χ-T) is shown in Figure 4(a). The paramagnetic susceptibility for a metal can generally be described by χ = χ0(1-aT2) [43]. The χ-T data are well fitted by this expression between 100 and 300 K, yielding χ0 = 2.05(1)×10-3 emu/mol and a = 4.2(1)×10-6 K-2. The low-temperature upturn of χ-T below 10 K can be roughly fitted using the Curie-Weiss law, 1/χ = (T–θW)/C, where θW is the Weiss temperature and C is the Curie constant. The fitted parameters are are θW = 0.7(3) K and C = 0.20(1) emu mol-1 K, corresponding to an effective magnetic moment μeff = 1.265 μB. This value is much smaller than the theoretical spin-only moment expected for PbCu3V4O12 with three localized Cu2+ (3d 9) and four V4+ (3d 1). Thus, the paramagnetic-like component most likely arises from a minor magnetic impurity, although it is difficult to identify such an impurity solely from the structural analysis. Similar Curie-like upturns at low temperatures have been reported in ACu3V4O12 (A = Na, Ca, Y) [14].No significant difference is observed between the ZFC and FC curves. The χ-1 - T plot is shown in Figure 4(b), together with those of CaCu3V4O12 and MnCu3V4O12 reproduced from the literature [14,15]. It is evident that χ-1 (T) for PbCu3V4O12 and CaCu3V4O12 deviates from Curie-Weiss behavior at high temperatures (above ~20 K), whereas MnCu3V4O12 exhibits a linear χ-1 - T relation. The localized 3d electrons of Mn2+ are believed to contribute to the Curie-Weiss behavior in MnCu3V4O12 [15]. In contrast, Ca2+ and Pb2+ at the A-site do not provide d electrons for magnetic interactions. The isothermal magnetization measured at various temperatures is shown in the inset of Figure 4(a). A linear field dependence starts to be observed from 50 K, whereas a slight deviation from linearity appears at 2 K, likely due to a minor magnetic impurity such as PbVO3 [46]. The overall magnetization is very small, consistent with the magnetic susceptibility data, indicating the absence of long-range magnetic ordering in PbCu3V4O12.Figure 5 (a) Specific heat Cp vs. T curve of PbCu3V4O12 measured in zero field. The inset shows an expanded view of the low-temperature region. (b) An approximate Debye fit to the Cp/T vs. T2 data near the low-temperature limit. The difference between the experimental Cp and the Debye fitting result (Cfit) is plotted as solid lines, with values shown on the right axis. (c, d) Low-temperature Cp vs. T data fitted using Cp = CDebye + CSchottky function for measurements collected at (c) H = 0 and (d) H = 90 kOe.In Figure 5(a), the temperature dependence of specific heat (Cp-T) is measured in zero magnetic field. Fitting the low-temperature data using an approximated Debye model, Cp/T = γ + β0T2, yields a Sommerfeld coefficient γ = 21.8(7) mJ/(mol K2) (equivalent to 5.45 mJ/(vanadium K2)), which is comparable to that of CaCu3V4O12 (= 30 mJ/(mol K2) or 7.5 mJ/(vanadium K2)) [14]. The γ values fall within the range typical of moderately correlated metallic perovskite oxides, such as CaVO3 and SrVO3 (γ = 8-9 mJ/(mol K2)) [47]. In contrast, typical weakly correlated metallic perovskites, for examples, Nb-doped SrTiO3 exhibits γ value below 2 mJ/(mol K2) [48]. On the other hand, several 3d transition-metal perovskite oxides, such as La1-xSrxTiO3 and Y1-xCaxTiO3, display significantly enhanced γ value, with their large effective carrier masses attributed to proximity to a metal-insulator transition [49,50]. In comparison, PbCu3V4O12 exhibits a moderate mass enhancement.The mass enhancement is further clarified by comparing the experimental γ value with the theoretical γ (DFT) value. Our DFT calculations, shown in Figure 6, yield N(EF) = 2.305 states/eV/f.u./spin. Using , the theoretical γ (DFT) is estimated to be 5.43 mJ/(mol K2). The experimental γ is enhanced by a factor of four relative to γ (DFT), comparable to the enhancement reported for the nickelate perovskite LaNiO3 [43]. The temperature-independent susceptibility χ0 can also be estimated from N(EF) using , giving χ0 (DFT) = 7.45×10-5 emu/mol. Interestingly, the ratio is significantly larger than , with values of 28 and 4, respectively. This indicates the presence of an additional mechanism that specifically enhances the magnetic susceptibility, rather than a renormalization arising solely from the effective mass enhancement. Electronic correlations may further amplify χ0 through the Stoner mechanism, as previously observed in the narrow-band system LaNiO3 [43]. Note that conventional DFT-based evaluations of magnetic order are essentially mean-field in nature and therefore have limitations in estimating magnetic ordering tendencies in systems with strong Coulomb interactions. A more reliable assessment of possible magnetic order in strongly correlated systems would require a beyond-DFT treatment that explicitly accounts for electronic correlations, which is left for future study.Figure 6 The band structure (a) and DOS (b) for PbCu3V4O12.The upturn of Cp/T below 6 K in zero field and the emergence of a broad hump under a magnetic field of 90 kOe, as shown in Figure 5(b), are reminiscent of a Schottky-like anomaly similar to those reported in oxides such as Sr3Cr2O8, Sr2YIrO6, and CaRuO3 [51-53].The upturn of Cp/T in zero field is likely the high-temperature tail of such a Schottky-like contribution, while the broad peak observed under 90 kOe shifts upward in temperature, reaching a maximum near 3.5 K. This field-dependent shift can be identified more clearly by subtracting the Debye component, CDebye = γT + β0T 3, from the experimental Cp, as shown in Figure 5(b). The resulting Cp – CDebye curves demonstrate that the broad peak moves to higher temperature with the application of a 90 kOe magnetic field. Furthermore, the low-temperature Cp data collected at 90 kOe are well reproduced by including a two-level Schottky contribution (CSch) [54]:The fitting results are shown in Figure 5(c) and 5(d). The presence of this Schottky-like anomaly is likely associated with a small amount of paramagnetic impurities, consistent with previous reports [51,52]. Paramagnetic centers are widely observed in oxide systems and may originate from paramagnetic impurities or intrinsic defects in the main phase of the sample. The latter may arise from deficiencies, chemical disorder, off-stoichiometry, and related effects.The family of A-site-ordered perovskite AA’3B4O12 has expanded significantly in recent decades, largely owing to advances in high-pressure and high-temperature synthesis. Although the physical properties vary widely, most members retain a robust cubic Im-3 structure independent of the specific A- or B-site compositions, providing an ideal platform to study property evolution. Table 2 summarizes the reported metallic members of this family and compares their synthesis conditions, resistivity (ρ) at 300 K, RRR, magnetic properties, Sommerfeld coefficients, and structural parameters.Table 2 Comparison of synthesis pressure, resistivity (ρ) at 300 K, estimated RRR for metallic compounds, magnetic susceptibility (χ) at 300 K, Sommerfeld coefficient (γ), and bond-valence sum (BVS) for metallic A-site-ordered perovskite oxides. All compounds listed in the table crystalize into cubic structure (Im-3) at room temperature. Compound Psynthesis(GPa) Lattice parameter (Å) ρ at 300K (mΩ cm) RRR value χ at 300 K(10-3 emu/mol) γ (mJ/(mol K2)) BVS at A-site Refs. PbCu3V4O12 8 7.33064(1) 4.95 1.27 1.4 21.8(7) 3.08 This work NaCu3V4O12 9 7.25332(1) 35.15 1.98 1.1 \ 1.52 [14] CaCu3V4O12 9 7.28094(1) 30.21 1.55 1.0 30 2.31 [14] MnCu3V4O12 12 7.2668(1) 1.75 1.43 12.1 \ 1.47 [15] CuCu3V4O12a 15 7.2483(1) 72.03 1.85 1.2 127(2) 1.09 [16] YCu3V4O12 9 7.2879(1) 1.17 1.86 1.1 \ 2.38 [14] CaCu3Cr4O12 6 7.253(3) 0.98 2.58 \ \ 2.35 [17] BiCu3Cr4O12 7.7 7.3028(1) 8 \ FIM b \ 3.11 [18] CaCu3Fe4O12 15 7.29692(5) MIT c \ FIM b \ 2.21 [5] CaCu3Co4O12 9 7.12260(5) 13 2.04 6.1 157.5(7) 2.65 [19] NaCu3Ru4O12 AP d 7.386(1) 0.45 5.55 2.9 75 1.24 [9,20,21] CaCu3Ru4O12 AP d 7.4098(8) 0.35 5.20 4.8 92 2.06 [13,22,23] LaCu3Ru4O12 AP d 7.477(1) 0.57 2.47 4.5 136 3.53 [9,20] PbCu3Ru4O12 12 7.47222(7) 15.56 5.82 4.3 98 2.75 [45] CaCu3Ir4O12 9 7.47380(6) 4.61 4.48 4.2 173 2.11 [24] LaCu3Ir4O12 9 7.524183(3) 670 1.41 5.5 336 3.31 [25]a BiCu3Cr4O12 and CaCu3Fe4O12 exhibit ferrimagnetic (FIM) transition at 190 K and 90 K, respectively.b CaCu3Fe4O12 exhibits metal-semiconductor transition at 90 K.c Ambient pressure (AP).In simple vanadate perovskite AVO3 (A = Ca, Sr, Pb), the crystal symmetry changes from the centrosymmetric structure (Pbnm or Pm-3m) for Ca and Sr to the noncentrosymmetric tetragonal P4mm for Pb due to the lone-pair electrons of Pb2+ [55-57]. This symmetry change accompanies marked differences in physical properties: CaVO3 and SrVO3 are metallic and no long-range magnetic ordering, whereas PbVO3 is insulating and exhibits two-dimensional antiferromagnetism. The lone pair of Pb2+ can narrow the π* bandwidth through Pb-O covalency competing with V-O bonding [58]. However, introducing Pb2+ at the A-site in AA’3B4O12 does not reduce the conductivity of PbCu3V4O12; its resistivity is nearly an order of magnitude lower than that of CaCu3V4O12 [14].Figure 7 Evolution of lattice parameter, bond lengths, and bond angles in ACu3V4O12 (A = Cu, Mn, Ca, Pb) as a function of A-site ionic radius.Unlike the simple perovskite ABO3, replacing the A-site with Pb in AA’3B4O12 does not break cubic symmetry. Although ACu3V4O12 (A = Cu, Mn, Ca, Pb) all remain cubic, the lattice parameter of PbCu3V4O12 deviates from the expected ionic-radius trend and is larger than anticipated, as shown in Figure 7. This suggests that lattice expansion is not caused solely by the larger ion occupied at A-site, but also by local structural modifications. The A-O bond length is indeed enlarged by Pb2+ and exceeds the expected value, leading to an unusually high BVS (= 3.08). Surprisingly, the Cu-O bond is also significantly elongated in PbCu3V4O12, and correspondingly, V-O bond lengths deviate from the trend observed in other ACu3V4O12 compounds. Meanwhile, the V-O-V bond angle in PbCu3V4O12 is less bent than in its analogues. The effect of Pb2+ substitution on the crystal structure has been investigated through a comparison between Sr1-xPbxRuO3 and Sr1-xBaxRuO3 [59]. It was found that although Pb and Ba substitution increase the average ionic radius, they induce distinctly different trends in the lattice parameters. This indicates that the structural effect of Pb2+ substitution cannot be explained solely by a simple steric effect. The structural behavior observed in PbCu3V4O12 is consistent with this finding reported for ruthenate perovskite systems.Metallic vanadate perovskites CaVO3 and SrVO3 exhibit moderate enhanced Sommerfeld coefficients (γ = 8-9 mJ/(mol K2)) [47], smaller than those of strongly correlated systems such as CaRuO3 and SrRuO3 (γ =30- 90 mJ/(mol K2)) [60,61] but clearly larger than weakly correlated metals like sodium (~1 mJ/(mol K2)). The A-site-ordered vanadates ACu3V4O12 (A = Cu, Ca, Pb) display γ values comparable to those of AVO3. CaCu3Ru4O12, one of the most studied A-site-ordered perovskites, is known for its heavy-fermion behavior arising from hybridization between localized Cu2+ (3d9) moments and itinerant Ru-4d electrons [13,62,63]. By analogy, the moderately enhanced γ in PbCu3V4O12 may reflect hybridization between localized Cu-3d moments and itinerant V-3d electrons. Because V4+ has only one 3d electron and the 3d orbitals are more localized than Ru-4d, the interaction is weaker. Nevertheless, γ values as large as 20-30 mJ/(mol K2) remain rare among 3d transition-metal oxides.4. ConclusionIn conclusion, the A-site-ordered perovskite PbCu3V4O12 was successfully synthesized under high-pressure and high-temperature conditions and confirmed to crystallize in a cubic Im-3 structure based on high-resolution synchrotron XRD. Its lattice parameter, A-O, Cu-O, V-O bond lengths, and V-O-V bond angle clearly deviate from the ionic-radius trend in the ACu3V4O12 series, indicating local structural modifications associated with the Pb2+ lone-pair electrons. Transport, thermoelectric, and magnetic measurements reveal conducting behavior without long-range magnetic ordering, while specific-heat and DFT analyses show moderate mass enhancement and an unusually amplified magnetic susceptibility, pointing to correlation effects beyond simple mass renormalization. These results identify PbCu3V4O12 as a rare 3d-electron metallic vanadate with moderate correlations and highlight the role of Pb-induced local structural distortions as a potential design strategy in perovskite-related materials.ASSOCIATED CONTENTSupporting InformationFigures and Tables showing XRD patterns for samples synthesized using different starting material ratios, additional structure refinement results of synchrotron XRD, first derivative of ρ(T) as a function of temperature and SEM-EDS elemental mapping of PbCu3V4O12 powder sample. AUTHOR INFORMATIONCorresponding Author* Jie ChenE-mail: jiechen.phy@bit.edu.cnZhiyan ShaoE-mail: 3120225763@bit.edu.cnMeiling JinE-mail: jinml@bit.edu.cnJiabin QiaoE-mail: jiabinqiao@bit.edu.cnXiang LiEmail: xiangli@bit.edu.cnNotesThe authors declare no competing financial interests.Author ContributionsThe manuscript was written through contributions from all the authors. All authors have given their approval for the final version of the manuscript.ACKNOWLEDGMENTSThis work was supported in part by the National Key R&D Program of China (Grant Nos. 2023YFA1406002, 2020YFA0308801), the National Natural Science Foundation of China (NSFC) (Grant Nos. 12174025, 12321004, 12204045), and the CAS Superconducting Research Project (Grant No. SCZX-0101). X. L. was supported by the Beijing Institute of Technology Research Fund Program (Grant No. 2023CX01027). J. C. and J. Q. were supported by the Beijing Institute of Technology Research Fund Program for Young Scholars. M. J. was supported by the Beijing Institute of Technology Laboratory Research Project (Grant No. 2023BITSYB07). F.Y. was supported by the National Natural Science Foundation of China (NSFC) (Grant Nos.12574141, 12234016, 12074031). Synchrotron radiation experiments were conducted at the powder diffraction beamline BL02B2 at SPring-8 with the permission from the Japan Synchrotron Radiation Research Institute (Proposal Number: 2024B1825). We thank Dr. S. Kobayashi and Dr. Y. Mori for their help at BL02B2 of SPring-8. The Analysis & Testing Center in the Beijing Institute of Technology and the Synergetic Extreme Condition User Facility (SECUF, https://cstr.cn/31123.02.SECUF) are also acknowledged.References[1] G. King and P. M. Woodward, Cation ordering in perovskites, Journal of Materials Chemistry 20, 5785 (2010).[2] L. T. Nguyen and R. J. Cava, Hexagonal perovskites as quantum materials, Chemical Reviews 121, 2935 (2021).[3] Y. Shimakawa, A-site-ordered perovskites with intriguing physical properties, Inorganic Chemistry 47, 8562 (2008).[4] A. A. Belik, Rise of A-site columnar-ordered A2A’A’’B4O12 quadruple perovskites with intrinsic triple order, Dalton Transactions 47, 3209 (2018).[5] Y. 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