A high-resolution neutron diffraction and electron diffraction study of the structure and phase transitions in AgTaO3

The high temperature phase transition behavior of the quantum paraelectric material, AgTaO3, has previously been debated in the literature. To elucidate the phase transitions of AgTaO3, we used neutron powder diffraction and established the phase transition sequence to be SCHEME 1. Phase transition of AgTaO3 as determined by examination of neutron powder diffraction patterns between room temperature and 700 °C. The temperatures for the two higher temperature transitions were also confirmed by differential scanning calorimetry. While the current neutron diffraction and published x-ray results are similar, critical analysis of superlattice reflections concluded the orthorhombic phase to be Ibmm, instead of Cmcm previously considered. The room temperature structure of AgTaO3 is difficult to characterize using powder diffraction due to the presence of domain wall artifacts. This was resolved by employing 3D electron diffraction on powdered AgTaO3 samples, indicating that the sample is rhombohedral at room temperature.