Сегнетоэлектрические фазовые переходы в Sr-=SUB=-9-=/SUB=-Tm(VO_4)-=SUB=-7-=/SUB=- при замещении стронция на кальций и свинец release_whdmj3zqive7vekh7kgjcidzve

Abstract

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 varies 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.
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