Experimental verification of the ab initio phase transition sequence in SrZrO3 and comparisons with SrHfO3 and SrSnO3

We present detailed Raman studies of SrZrO3 (SZO) that show three anomalies in Raman modes: One has a small jump in frequency omega, one has its intensity vanish, and a third has a sharp change in temperature derivative d omega(T)/dT from flat below T=600 K to a Curie-Weiss dependence above 600 K with extrapolation to zero frequency at the known transition temperature T=970 K, thereby proving the latter to be displacive. In addition, the P4mm ferroelectric phase predicted at high stresses has preliminary support from polarization-voltage experiments. The inference of a new transition in the temperature region 600-650 K is in disagreement with neutron studies. Comparisons are given for family member SrSnO3 and SrHfO3, and we discuss the different conclusions of Kennedy and Knight. We show that a known transition in SrHfO3 is also displacive with a well-behaved soft mode.