Temperature-dependent Raman spectra of KTaO3 crystal and melt along with its phonon and electronic properties

In situ high temperature Raman spectra of KTaO3 crystal and melt were measured over the wavenumber range of 100–1600 cm−1 from ambient temperature to 1723 K by intensified charge coupled device (ICCD) coupled with high temperature observational furnace. The band structure, density of states (DOS), phonon density of states (PDOS) and phonon dispersion of KTaO3 crystal were calculated by density functional theory (DFT). According to the theoretical calculation, strong covalence of Ta-O bonds and band gap were confirmed, phonon branch assignments for the second order Raman spectrum of KTaO3 crystal were made. A series of model clusters were constructed and their Raman spectra were simulated by DFT to determine the microstructures of KTaO3 melt. The relation between TaO bond lengths and characteristic Raman-active vibration wavenumbers of the molten KTaO3 has been investigated by which Raman spectrum of KTaO3 melt was deconvoluted by a sum of Gaussian peaks based on DFT results. Results showed that the lattice framework collapsed and the second order Raman peaks disappeared while the crystal being melt. Different from previous conclusion that there was only one type of TaO complex, a mixture of TaO anion complexes was proved to coexist in the molten KTaO3 while disproportionation equilibrium being reached, and those complexes were identified in this work.