BARIUM AND CALCIUM NIOBATE CERAMICS: SPECIFIC FEATURES OF THEIR STRUCTURE

В работе получены и исследованы образцы керамики на основе ниобата бария - кальция CaBaNbO, с различным процентным соотношением бария и кальция (с x = 1; 0,9; 0,8; 0,7; 0,6; 0,5; 0,4; 0,3; 0,2; 0,1 и 0 ). Исследовано влияние температуры спекания на структуру и диэлектрические свойства керамики. Одна партия образцов спекалась при температуре 1100°С, вторая при температуре 1250°С. Показано, что температуры спекания 1100 °С не достаточно для получения хороших сегнетоэлектрических свойств, а процесс рекристаллизации зерен не завершен. Согласно исследованиям элементного состава, у образцов, спеченных при температуре 1250 °С с содержанием Ca≥0,5, атомы Ba присутствуют не во всех зернах, что оказывает влияние и на ход температурных зависимостей диэлектрической проницаемости. По диэлектрическим свойствам выделяется образец с x = 0,3. We obtained and studied the samples of ceramics based on barium niobate and calcium niobate CaBaNbO with different percentages of barium and calcium (x = 1; 0,9; 0,8; 0,7; 0,6; 0,5; 0,4; 0,3; 0,2; 0,1 and 0 ). The effect of the sintering temperature on the structure and dielectric properties of ceramics has been investigated. One batch of the samples was sintered at a temperature of 1100 °C, the second at 1250 °C. We have shown that the sintering temperature of 1100 °C is not enough to obtain good ferroelectric properties, and the process of grain recrystallization is not completed. According to studies of the elemental composition, in samples sintered at a temperature of 1250 °C with the Ca content greater than 0,5, Ba atoms are not present in all grains, which also affects the course of the temperature dependences of the dielectric constant A sample with x = 0,3 is distinguished by its dielectric properties.

Study of Luminescent Properties of CaNb2O6:Yb, Er, Tm

We used solid phase synthesis at 1200 °C to create a luminophore based on CaNb2O6 and activated by ytterbium, erbium, and thulium ions. We present X-ray phase analysis results for the CaNb2O6:Yb, Er, Tm compound. The X-ray diffraction patterns obtained do not contain reflexes belonging to the intermediate phases. We investigated spectral properties of a calcium niobate-based luminophore upon excitation by a 940 nm laser. There are bands in the visible and IR regions to be found in the luminescence spectra. The up-conversion (anti-Stokes emission) luminescence spectrum comprises three bands peaking at 560, 676 and 807 nm. In the IR range, there are three peaks to be detected in the luminescence spectrum at 1010, 1540 and 1812 nm. We established the luminescence variation patterns for compounds based on CaNb2O6:Yb, Er, Tm. We determined the optimum Tm3+ concentration in the system that makes it possible to achieve the highest luminescence efficiency in the 1640--2000 nm range peaking at 1812 nm. We considered an energy transfer mechanism involving Yb3+ and Er3+ as luminescence stabilisers in a thulium ion. Employing erbium as an additional sensitiser allowed the luminescence intensity in the 1812 nm band to be increased by 1.5 time