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231. Structural and dielectric studies of the phase behaviour of the topological ferroelectric La1−xNdxTaO4.

Author

Cordrey, Keith J., Stanczyk, Magda, Dixon, Charlotte A. L., Knight, Kevin S., Gardner, Jonathan, Morrison, Finlay D., and Lightfoot, Philip

Subjects
LANTHANUM compounds, CRYSTAL structure, DIELECTRIC properties, PHASE transitions, EFFECT of temperature on metals
Abstract

The layered perovskite LaTaO4 has been prepared in its polar orthorhombic polymorphic form at ambient temperature. Although no structural phase transition is observed in the temperature interval 25° C ＜ T ＜ 500 °C, a very large axial thermal contraction effect is seen, which can be ascribed to an anomalous buckling of the perovskite octahedral layer. The non-polar monoclinic polymorph can be stabilised at ambient temperature by Nd-doping. A composition La0.90Nd0.10TaO4 shows a first-order monoclinic-orthorhombic (non-polar to polar) transition in the region 250° C ＜ T ＜ 350 °C. Dielectric responses are observed at both the above structural events but, despite the ‘topological ferroelectric’ nature of orthorhombic LaTaO4, we have not succeeded in obtaining ferroelectric P–E hysteresis behaviour. Structural relationships in the wider family of AnBnX3n+2 layered perovskites are discussed. [ABSTRACT FROM AUTHOR]

Published
2015
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232. Novel S = 1/2 Kagome Lattice Materials: Cs2TiCu3F12 and Rb2TiCu3F12.

Author

Downie, Lewis J., Ardashnikova, Elena I., Tang, Chiu C., Vasiliev, Alexandre N., Berdonosov, Peter S., Dolgikh, Valery A., de Vries, Mark A., and Lightfoot, Philip

Subjects
CRYSTAL lattices, PHASE transitions, CRYSTAL structure, SINGLE crystals, ANTIFERROMAGNETIC materials, FLUORIDES
Abstract

Two new members of the A2B'Cu3F12 family of kagome-related materials have been prepared, in order to further understand the crystal-chemical relationships, phase transitions and magnetic behaviour within this family of potentially frustrated S = 1/2 two-dimensional quantum magnets. Cs2TiCu3F12 adopts a crystal structure with the ideal kagome lattice topology (space group R...m) at ambient temperature. Diffraction studies reveal different symmetry-lowering structural phase transitions in single crystal and polycrystalline forms at sub-ambient temperatures, with the single crystal form retaining rhombohedral symmetry and the powder form being monoclinic. In both cases, long-range antiferromagnetic order occurs in the region 16-20 K. Rb2TiCu3F12 adopts a distorted triclinic structure even at ambient temperatures. [ABSTRACT FROM AUTHOR]

Published
2015
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