By solid-phase synthesis at 1373 K in Sr9-xMexTm (VO4)7 systems the solid solutions with Me = Ca (0≤ x≤2) and Me = Pb (0≤ x≤1) were obtained. Single-phase samples at room temperature are isostructural to the Ca3(VO4)2 ferroelectric (space group (sp.gr.) R3c, Z = 6). Substances are characterized by X-ray phase analysis (XRD), second optical harmonic generation (SHG), and dielectric spectroscopy. The intensity of the SHG signal change depending on the substitution cation and its concentration

more »

... es in the range of 30-50 units relative to the quartz standard. A reversible ferroelectric phase transition was found in the temperature range 850–960 K. The transition is accompanied by a sharp maximum in the temperature dependence of the dielectric constant. The absence of a SHG signal above the transition temperature indicates the centrosymmetry of the paraelectric phase.