Features of the Crystal Structure and Vibrational Spectra of Ba1.65Sr3.35Nb10O30–Ba4Na2Nb10O30 Barium-Strontium Niobates with the Structure of Tetragonal Tungsten Bronze

Abstract

The crystal structure and vibrational spectra of Ba_1.65Sr_3.35Nb₁₀O₃₀–Ba₄Na₂Nb₁₀O₃₀ barium-strontium niobates are investigated by neutron diffraction and Raman spectroscopy in the concentration range x = 0–1 with steps of 0.1 and 0.05. All compounds under study have a structure of the tetragonal tungsten-bronze type with the space group of P4mm symmetry. The concentration dependences of the crystal-cell parameters, interatomic bonds, and vibrational modes for a number of solid solutions of the (1–х)Ba_1.65Sr_3.35Nb₁₀O₃₀–хBa₄Na₂Nb₁₀O₃₀ system are obtained. Anomalies in the behavior of the crystal parameters and vibrational modes are observed for the concentration dependences at x ~ 0.5. This may be due to a change in the nature of the sodium occupation of vacancies in various crystallographic positions of the tetragonal structure.