The influence of Sr(Ca)2Nb2O7 on the phase formation and the structure of solid solutions based on the sodium-kalium niobate

(1- x )KNbO 3 - x NaNbO 3 system is one of the most learned among lead-free ceramics. This system is promising for potential use in piezoelectric technology and the replacement of lead-containing elements in such devices. However, despite many works aimed at the solution of this problem, at the moment, no lead-free materials with the properties comparable to the lead-containing piezo-ceramics were produced. It is caused by various technological difficulties of creating solid solutions (SS) based on the lead-free compositions such as alkaline components volatility and the strongest dependence of the observed properties on the production conditions (thermodynamic history). One of the techniques applied to improve processability and SS stability as well as to improve electrophysical properties is modifying. The paper deals with the study of the influence of calcium and strontium pyroniobates additives on the structure and properties of (1- x )KNbO 3 - x NaNbO 3 system. The conditions of synthesis and sintering for each solid solution of (1- x-у )KNbO 3 - y NaNbO 3 - x (Sr/Са) 2 Nb 2 O 7 systems are optimized. The author carried out the X-ray diffraction and radiographic analysis of the produced items, analyzed the dependence of the parameters, cell volume, and the ceramics densities on the concentration of added (Sr/Са) 2 Nb 2 O 7 component. The study determined that the increase in the content of calcium and strontium pyroniobates in the interval of 0≤х≤10 % leads to the appearance of several phase transitions caused by the structural transformation in the (1- x-у )KNbO 3 - y NaNbO 3 - x (Sr/Са) 2 Nb 2 O 7 systems. The symmetry of the abovementioned systems changes in different ways. The doping with strontium pyroniobate causes the tetragonal structure distortion and the doping with calcium pyroniobate leads to the formation of the cubic lattice. The study showed as well that the adding of (Sr/Са) 2 Nb 2 O 7 pyroniobates to the (1- x )KNbO 3 - x NaNbO 3 system above 2.5 % significantly reduces the density of the produced ceramics.