Structure Determination and Analysis of the Ceramic Material La0.987Ti1.627Nb3.307O13 by Synchrotron and Neutron Powder Diffraction and DFT Calculations

In this paper, the ternary system La2O3-TiO2-Nb2O5 is studied to find new ternary phases with useful electrical properties. The solid solution La3-xTi5-3xNb10-2xO39.5-12.5x was recently identified, and this study focuses on the structural characterization of this solid solution with x = 0.04. The crystal structure, representing a new structural type, was determined from synchrotron and neutron powder diffraction data. The unit cell parameters are a = 7.332 A, b = 7.421 A, c =10.673 A, a = 84.15 degrees, beta = 80.16 degrees, ? = 60.37 degrees, and space group P(1). The titanium and niobium atoms are disordered in five different crystallographic sites coordinated octahedrally by oxygen atoms. The eight-coordinated La atoms are embedded in the octahedral framework. Ti and Nb preferentially occupy different sites, and this feature was studied using periodic density functional theory methods. Energies of possible Ti/Nb distributions were calculated and the results agree well with the site occupancies obtained by combined Rietveld refinement of synchrotron and neutron powder diffraction patterns. The geometries optimized by DFT also agree well with the structural parameters determined by diffraction. The general agreement between the theoretical calculations and the experimental data jus-tifies the quantum chemical methods as reliable complementary tools for the structural investigation of ceramic materials.

Automated summary

This study focuses on the structural characterization of the solid solution La3-xTi5-3xNb10-2xO39.5-12.5x with x = 0.04 in the ternary system La2O3-TiO2-Nb2O5. The crystal structure was determined using synchrotron and neutron powder diffraction data, revealing a new structural type. The octahedrally coordinated titanium and niobium atoms are disordered in five different crystallographic sites, while the La atoms are embedded in the octahedral framework. The theoretical calculations based on density functional theory agree well with the experimental data, validating its reliability as a complementary tool for structural investigation of ceramic materials.