Beyond the ionic radii: A multifaceted approach to understand differences between the structures of LnNbO4 and LnTaO4 fergusonites

Mullens, Bryce G.; Saura-Múzquiz, Matilde; Marlton, Frederick P.; Avdeev, Maxim; Brand, Helen E. A.; Mondal, Subrata; Vaitheeswaran, G.; Kennedy, Brendan J.

doi:10.1016/j.jallcom.2022.167399

Cited by 7 publications

(17 citation statements)

References 72 publications

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“…This shows that all the compounds crystallize in a monoclinic structure with space group I2/a (#15). The obtained lattice parameters and atomic positions are summarized in table 1, and are in good agreement with previous reports [26,29]. Figure 2(a) represents the crystal structure of the studied compounds, consisting of (Gd/Dy)O 8 and (Ta/Nb)O 6 units.…”

Section: Structural Analysissupporting

confidence: 88%

Enhanced cryogenic magnetocaloric performance and the existence of short-range magnetic correlations in frustrated diamond geometries

Kumar,

Mukherjee

2024

J. Phys. D: Appl. Phys.

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Magnetocaloric effect in cryogenic temperature regime has gained enormous attention due to its application in the field of cryogenic refrigeration technology, which is required for quantum computing, space sciences and basic research activities. In this context, Gd and Dy based frustrated systems are considered as promising cryogenic magnetocaloric materials. Hence, magnetic and magnetocaloric properties of GdTaO4, GdNbO4 and DyNbO4 are comprehensively investigated. Structural analysis suggest that these compounds crystallize in monoclinic structure, wherein magnetic ions form an elongated diamond geometry. The analysis of magnetization, heat capacity and field dependent magnetic entropy change confirm the presence of short-range magnetic correlations in these compounds. Additionally, a remarkably large magnetic entropy change, and relative cooling power are noted. The mechanical efficiency is found comparable (or even better) to those reported for good magnetic refrigerants. Our study suggests that GdTaO4, GdNbO4 and DyNbO4 can be regarded as promising cryogenic magnetic refrigerant materials.

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Section: Structural Analysissupporting

confidence: 88%

Enhanced cryogenic magnetocaloric performance and the existence of short-range magnetic correlations in frustrated diamond geometries

Kumar,

Mukherjee

2024

J. Phys. D: Appl. Phys.

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“…The relative density was calculated as the ratio of the experimental density and the theoretical density of the sample obtained from previous synchrotron X-ray diffraction measurements. 49,55 The relative densities are reported in the SI (Table S4). Before each measurement, pellets were coated in a conductive Pt paste and reheated to 1000 °C for 2 h to cure the paste.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…The same phenomenon has been previously observed, where the B−O(2') long bond is shorter in TaO 6 than the corresponding NbO 6 polyhedra (Table 1). 44,49,55 The temperature dependence of the appropriately scaled lattice parameters is shown (Figure 6). Upon heating, the P2/c phase undergoes expansion in all three lattice directions.…”

Section: Chemistry Of Materialsmentioning

confidence: 99%

“…Evidently, the conclusions drawn by Huse et = Nb, Ta) structures, the Nb 5+ and Ta 5+ cations are at slightly different positions in the isostructural I2/a phases due to the differences in the 4d and 5d orbitals. 49 This leads to a larger B−B separation in B 5+ = Ta compared to Nb, potentially contributing to the higher ionic conductivity exhibited in the HoTaO 4 structures. The conductivity pathway is different in the P2/c structure as a consequence of the different arrangement of the TaO 6 chains (Figure 1), potentially explaining the difference in conductivity between the I2/a and P2/c structures.…”

Section: Chemistry Of Materialsmentioning

confidence: 99%

“…49 A recent study by Mullens et al also observed that the synthesis of LnTaO 4 (Ln 3+ = Tb−Ho) was sensitive to the thermal history of the material, with lower temperatures favoring the P2/c structure and higher temperatures favoring I2/a. 49 In addition to their crystal chemistry, LnTaO 4 materials have shown different behavior at elevated temperatures. The I2/a to I4 1 /a phase transition has been reported in several LnBO 4 (B 5+ = Nb, Ta) compounds and is dependent on the size of the Ln 3+ cation (LaNbO 4 T c = ∼480 °C, HoNbO 4 T c = ∼810 °C) and on the choice of B-site cation (NdNbO 4 T c = ∼660 °C, NdTaO 4 T c = ∼1220 °C).…”

Section: ■ Introductionmentioning

confidence: 96%

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Variable Temperature In Situ Neutron Powder Diffraction and Conductivity Studies of Undoped HoNbO₄ and HoTaO₄

Mullens,

Saura-Múzquiz,

Cordaro

et al. 2024

Chem. Mater.

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Neutron powder diffraction data has been used to quantify the monoclinic (space group I2/a) to tetragonal (I4 1 /a) phase transition that occurs at 775 °C in HoNbO 4 and 1300 °C in HoTaO 4 . In both cases, deviation from second-order behavior is evident. The LnTaO 4 (Ln = Tb−Er) family of oxides has the potential to adopt one of monoclinic, I2/a or P2/c, structures depending on the synthesis conditions. The monoclinic P2/c polymorph of HoTaO 4 undergoes an irreversible first-order phase transition to the high-temperature I4 1 /a scheelite-type structure upon heating, with the monoclinic I2/a phase recovered upon cooling. This is the first direct evidence of this irreversible phase transition and implies a maximum heating temperature to synthesize the P2/c phase for potential ionic conductivity applications. Heating a green powder mixture of Ho 2 O 3 + Ta 2 O 5 revealed a complex series of phase transformations, including the observation of a weberite-type Ho 3 TaO 7 intermediate between 1200 and 1390 °C that was not observed upon cooling. Coupled with electrochemical impedance spectroscopy measurements, this diffraction data provides a structural model that explains the higher mobility of charge carriers in LnTaO 4 materials that can be used to identify dopants and improve their ionic conductivity and applicability. Undoped HoNbO 4 and HoTaO 4 are poor conductors, and the activation energy of tetragonal HoNbO 4 is greater than that of the monoclinic polymorphs. Oxygen ion and proton conductivities of the undoped structures occur via interstitial oxygen sites (∼10 −6 S cm −1 at 800 °C), providing a potential avenue to improve their application in practical devices such as solid oxide fuel cells.

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Intercalated Water Drives Anomalous Thermal Expansion in the Tetragonal Zircon Structured Bismuth Vanadate BiVO₄Photocatalyst

Mullens,

Marlton,

Nicholas

et al. 2024

Chemistry An Asian Journal

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The thermal transformation of zircon to scheelite in BiVO4 was studied by in‐situ Synchrotron X‐ray diffraction and TGA/FTIR analysis. Upon heating, the tetragonal zircon polymorph of BiVO4 (tz‐BiVO4) transitioned to the tetragonal scheelite (ts‐)polymorph between 693‐773 K, then to monoclinic fergusonite (mf) polymorph upon cooling. An anomaly in thermal expansion was observed between 400‐500 K, associated with loss of H2O/NH4+. Heating tz‐BiVO4 resulted in contraction of the V‐O bond distance and VO4 polyhedra volume due to rotation of the VO4. Attempts to study this by neutron diffraction failed due to the large incoherent scatter from the hydrogenous species. Efforts to remove these species while maintaining the tz‐BiVO4 structure were unsuccessful, suggesting they play a role in stabilizing the zircon polymorph. The local structure of both mf‐BiVO4 and tz‐BiVO4 were investigated by X‐ray Pair Distribution Function analysis.

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Beyond the ionic radii: A multifaceted approach to understand differences between the structures of LnNbO4 and LnTaO4 fergusonites

Cited by 7 publications

References 72 publications

Enhanced cryogenic magnetocaloric performance and the existence of short-range magnetic correlations in frustrated diamond geometries

Enhanced cryogenic magnetocaloric performance and the existence of short-range magnetic correlations in frustrated diamond geometries

Variable Temperature In Situ Neutron Powder Diffraction and Conductivity Studies of Undoped HoNbO₄ and HoTaO₄

Intercalated Water Drives Anomalous Thermal Expansion in the Tetragonal Zircon Structured Bismuth Vanadate BiVO₄Photocatalyst

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Beyond the ionic radii: A multifaceted approach to understand differences between the structures of LnNbO4 and LnTaO4 fergusonites

Cited by 7 publications

References 72 publications

Enhanced cryogenic magnetocaloric performance and the existence of short-range magnetic correlations in frustrated diamond geometries

Enhanced cryogenic magnetocaloric performance and the existence of short-range magnetic correlations in frustrated diamond geometries

Variable Temperature In Situ Neutron Powder Diffraction and Conductivity Studies of Undoped HoNbO4 and HoTaO4

Intercalated Water Drives Anomalous Thermal Expansion in the Tetragonal Zircon Structured Bismuth Vanadate BiVO4Photocatalyst

Contact Info

Product

Resources

About

Variable Temperature In Situ Neutron Powder Diffraction and Conductivity Studies of Undoped HoNbO₄ and HoTaO₄

Intercalated Water Drives Anomalous Thermal Expansion in the Tetragonal Zircon Structured Bismuth Vanadate BiVO₄Photocatalyst