Cluster Calculations of Electric-Field-Gradients at the Ta Site for the Ferroelectric LiTaO 3 Crystal

Abstract

Ab initio cluster calculations of electric-field-gradients at the Ta site in the ferroelectric LiTaO 3 crystal have been carried out for the temperature range 160 to 940 K. The calculations were made for the (TaO 6 ) −7 cluster using the WT basis set for the tantalum and TZV basis set augmented with the polarization d-function (0.85) for the oxygen. The results of calculations of the V zz temperature dependence agreed well with experimental data.

Unveiling the Defect Structure of Lithium Niobate with Nuclear Methods

“…As thermal lattice expansion alone would make the EFG increase moderately with temperature, the main contribution to the EFG comes from the displacement of the atoms. More advanced ab initio cluster calculations of Shelyapina et al [92] reproduced the essential features of the EFG temperature dependence up to T C . The temperature dependence of the nuclear quadrupole interaction at the Li site was measured using NMR, MS and PAC methods in LN and LT. 7 Li NMR measurements in single-crystalline LN were reported by Halstead [39] below TC, up to ≈950 K. A linear increase of the QIF was observed in this temperature range.…”

“…As thermal lattice expansion alone would make the EFG increase moderately with temperature, the main contribution to the EFG comes from the displacement of the atoms. More advanced ab initio cluster calculations of Shelyapina et al [92] reproduced the essential features of the EFG temperature dependence up to TC. There is no agreement among the theoretical calculations on the phase transition.…”

Local structure in perovskite relaxor ferroelectrics: high-resolution 93Nb 3QMAS NMR

“…To better understand the effects of nBn configurations on P Q ab initio calculations of the electric field gradient should be carried out using either the MO LCAO-SCF (molecular orbitals-linear combinations of atomic orbitals-self-consistent field) or LDA LAPW (local density approximation using extended general potential linearized augmented plane wave method) approach. The former approach has been successfully applied to calculate the EFGs at the transition-metal sites in LiNbO 3 and LiTaO 3 crystals and at the aluminum sites in mixed ionic crystals CaRAlO 4 (R ¼ La, Pr, Eu, Y) [30,31]; the latter approach has been applied to calculate the EFGs at the cation sites in BaTiO 3 and KNO 3 [32,33].…”