Structural and dielectric studies of the phase behaviour of the topological ferroelectric La1-xNdxTaO4
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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.
Cordrey , K J , Stanczyk , M , Dixon , C A L , Knight , K S , Gardner , J , Morrison , F D & Lightfoot , P 2015 , ' Structural and dielectric studies of the phase behaviour of the topological ferroelectric La 1-x Nd x TaO 4 ' , Dalton Transactions , vol. 44 , no. 23 , pp. 10673-10680 . https://doi.org/10.1039/c4dt03721a
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DescriptionWe thank the University of St Andrews and EPSRC (via DTG studentships to CALD and JG) for funding,
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