OPTIMIZATION OF TECHNOLOGY FOR PRODUCING A COMPOSITE BASED ON BARIUM FERRITE AND BARIUM TITANATE

В работе показано, что в результате спекания образцов композита титанат бария (80 объемных %) - феррит бария (20 объемных %) в фарфоровом тигле при температуре 1300 °С возникает эвтектика. В результате сравнения свойств образцов, полученных при различных температурах спекания, установлено, что оптимальные свойства имеют образцы, спеченные при 1250 °С. Проведено сравнение структуры и диэлектрических свойств образцов керамики титаната бария и композита титанат бария (80 объемных %) - феррит бария (20 объемных %), спеченных при температуре 1250°С. Показано, что добавление в состав титаната бария 20% феррита бария повышает значение диэлектрической проницаемости, пироэлектрического коэффициента и пьезоэлектрического модуля d композита в 1,5 - 2 раза по сравнению с керамикой титаната бария, тогда как значение пьезоэлектрического модуля d остается без изменения. Введение в состав керамики титаната бария 20 % феррита бария достаточно для того, чтобы полученный композит имел магнитные характеристики, соответствующий чистому ферриту бария. It is shown in the work that as a result of sintering of composite samples of barium titanate (80 vol. %) - barium ferrite (20 vol. %) in a porcelain crucible at a temperature of 1300 °C, a eutectic appears. As a result of comparing the properties of the samples obtained at different sintering temperatures, it was found that the samples sintered at 1250 °C have optimal properties. The structure and dielectric properties of barium titanate ceramic samples and barium titanate (80 vol. %) - barium ferrite (20 vol. %) composite sintered at a temperature of 1250 °C are compared. It has been shown that the addition of 20% barium ferrite to the composition of barium titanate increases the dielectric constant, pyroelectric coefficient, and piezoelectric modulus d of the composite of 1,5 - 2 times compared to barium titanate ceramics, while the value of the piezoelectric modulus d remains unchanged. The introduction of 20 % barium ferrite into the barium titanate ceramics is sufficient for the resulting composite to have magnetic characteristics corresponding to pure barium ferrite.

Dependence of the dielectric properties of barium titanate ceramics and a composite based on it on the sintering temperature

In this paper, we compare the structure and dielectric properties of the samples of barium titanate ceramics that have been sintered at temperatures of 1100, 1150, 1200, 1250 and 1350 °C and dielectric characteristics of the samples of barium titanate (80 vol.%) — barium ferrite (20 vol.%). It is shown that only samples sintered at the temperature of 1250 and 1350 °C have polarization sufficient for the existence of the piezoelectric effect. For the same samples, the pyroelectric coefficient and reversal polarization significantly exceed those for samples sintered at lower temperatures. Analysis of the samples structure confirmed the dependence of the dielectric properties of the barium titanate ceramics on the grain size and, as a consequence, on the sintering temperature. Based on the studies carried out, the optimal temperature (1250 °С) for obtaining composite samples of barium titanate (80 vol.%) — barium ferrite (20 vol.%) was selected. The temperature dependence of the dielectric constant for the composite samples based on barium ferrite — barium titanate with a sintering temperature of 1250 °C is similar to the dependence for the BaTiO3 ceramic samples sintered at 1350 °C. At room temperatures, the permittivity of the composite samples is also significantly higher than that of the barium titanate ceramic samples obtained at the same sintering temperatures. The addition of barium ferrite to the barium titanate not only increased the permittivity of the composite, but also led to a diffusing of the ferroelectric phase transition and a shift in the temperature of the maximum of the dielectric constant by 10 degrees towards high temperatures.

Dielectric studies and AC conductivity of piezoelectric barium titanate ceramic polymer composites

In this work, ceramics barium titanate (BT) polymer composites were prepared with BT/polyvinyl alcohol (PVA) having a ceramic concentration of 10, 30, and 50% by weight using solution casting method. The prepared thin film samples were characterized by X-ray diffraction for phase analysis. Scanning electron microscope (SEM) studies on composite films revealed ceramic crystallites are well dispersed in the polymer matrix. The dielectric constant ( εr) and the AC conductivity at room temperature and at different frequencies (100 Hz–5 MHz) of the piezoelectric composites with different concentrations were investigated. The result shows that the dielectric constant of ceramic-PVA composites was found to increase as ceramic concentration increases and the dielectric loss tangent decreased with increasing concentration. AC conductivity of the composites increased with increasing frequency.

ANALYSIS OF CRACK INITIATION AND PROPAGATION IN PIEZOELECTRIC CERAMIC BY USING BOUNDARY ELEMENT METHOD

<p> <strong><span style="font-family: Times New Roman; font-size: small;">Abstract </span></strong></p><p><span style="font-family: Times New Roman;">The subject of this paper is the analysis of crack initiation and propagation in barium titanate ceramic using boundary element method. In micro-mechanical analyses, it is very important to have knowledge about the real microstructure of material. The barium titanate pellet was prepared using a solid-state technique. The boundary element method is used in order to be combined with three different grain boundary formulations for the investigation of micro-mechanics as well as crack initiation and propagation in piezoelectric actuator. In order to develop a numerical programming algorithm, suitable models of polycrystalline aggregate and representative volume elements have been prepared for boundary element analysis. </span></p>