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

• Structures Na0.99K0.01TaO3 studied using high resolution neutron diffraction.• Potassium doping is important in establishing phase separation between the Cmcm and Pbnm phases.• At 1% potassium doping does not impact either the sequence or temperatures of the high temperature phase transitions.

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 723 K. Chemical doping, does however, dramatically impact on the amount of the metastable Cmcm phase observed at room temperature.

Graphical abstractNeutron diffraction demonstrated that phase co-existence in NaTaO3 does not impact on the sequence or temperatures of the various high temperature phase transitions, suggesting impurities are critical to the observed phase separation.Figure optionsDownload full-size imageDownload as PowerPoint slide