Solid solutions Bi0.65Ba0.35-zSrzFe0.65Ti0.35O3 с 0 ≤ z ≤ 0.35: composition, structure,properties

The crystal structure of the solid solutions Bi0.65Ba0.35-zSrzFe0.65Ti0.35O3 within the dopant concentration range 0 ≤ z ≤ 0.35 was investigated based on the results of X-ray diffraction, infrared and Raman spectroscopy. The morphology and chemical composition of the solid solutions were studied using scanning electron microscopy and energy - dispersive X - ray spectroscopy. It is shown that all the studied compounds are characterized by high chemical homogeneity; an increase in the concentration of strontium ions leads to a decrease in the average crystallite size, while the morphology of crystallites remains practically unchanged. The obtained structural data allowed to estimate the changes in the crystal structure occurred within the region of the “rhombohedral - cubic” morphotropic phase boundary. The initial compound Bi0.65Ba0.35Fe0.65Ti0.35O3 is characterized by a two - phase structure, assuming a coexistence of the polar rhombohedral and cubic phases. Wherein the cubic phase is dominant in the initial compounds, and an increase in the concentration of Sr ions leads to the structural transition to the single - phase cubic state. An inhomogeneous structural state in the compounds under study has been determined to consist of the main matrix with paraelectric cubic structure, along with polar active nanometer - sized clusters having rhombohedral type of the unit cell. The presence of the nanosize polar clusters is confirmed by the results of dielectric measurements. The obtained data allowed to establish the evolution of the structural parameters during the phase transition from the rhombohedral to the cubic structure, as well as to determine the concentration region of the two - phase structural state and to specify the features of dielectric properties in the region of the morphotropic “rhombohedral - cubic” phase boundary.