The impact of room temperature polymorphism in K doped NaTaO3 on structural phase transition behaviour

Abstract

Temperature dependent high resolution neutron diffraction studies demonstrate that the sequence and temperatures of the crystallographic phase transitions in NaTaO3 are not impacted by doping with 1% K to form Na0.99K0.01TaO3. Rietveld analysis of the neutron diffraction data shows the structural transitions to be:Pbnm↔723 KCmcm↔803 KP4/nbm↔893 KPm3¯m. The two orthorhombic polymorphs, Pbnm and Cmcm, differ fundamentally in the distortion and tilting of the octahedra, such that they cannot be obtained from each other via a continuous phase transition resulting in their co-existence between RT and 723K. Chemical doping, does however, dramatically impact on the amount of the metastable Cmcm phase observed at room temperature.