Structural and dielectric studies of the phase behaviour of the topological ferroelectric La1-xNdxTaO4

摘要

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 degrees C < T < 500 degrees 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 monoclinicorthorhombic (non-polar to polar) transition in the region 250 degrees C < T < 350 degrees 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 A(n)B(n)X(3n+2) layered perovskites are discussed.