Structural peculiarities and point defects of undoped and Cr- and Ni-doped Sr0.61Ba0.39Nb2O6 crystals

Crystals of strontium barium niobate solid solutions, both nominally pure Sr0.61Ba0.39Nb2O6 and doped with transition metal (Cr3+ and Ni3+) ions, have been investigated by X-ray diffraction. The chemical composition of the undoped crystal was determined taking into consideration vacancies in niobium Nb(2) and oxygen sites and the statistical distribution of strontium in two (Sr(1) and Sr(2)) sites in the tetragonal tungsten bronze type crystal structure. It was established that the introduction of chromium or nickel oxides into the melt initial composition greatly influences the strontium and barium content in the crystals obtained and the distribution of these species in the crystallographic structure. The probability of finding the transition metal ions in regular and interstitial positions depending on their concentration and valence state is discussed.