Temperature Trends of the Permittivity in Complex Oxides of Rare-Earth Elements With Perovskite-Type Structure

Abstract

Ceramic materials based on complex oxides with both the perovskite structure (Ln 2/3 Nb 2 O 6 ) and the structure of tetragonal tungsten bronze (Ba 6−x Ln 8+2x/3 Ti 18 O 54 ) have been investigated over a wide frequency and temperature ranges. The results obtained for certain structures denote the presence of the temperature anomalies of dielectric parameters ( , tan δ). These anomalies occur over the wide frequency range including submilimeter (SMM) wavelength range, and are related neither with the processing peculiarities nor with the presence of the phase transitions. Temperature behavior of the permittivity has been considered in terms of the polarization mechanism based on the elastic-strain lattice oscillations. It has been assumed that the observed anomalies could be ascribed to a superposition of harmonic and anharmonic contribution to lattice oscillations that determines τ sign and magnitude.

TEMPERATURE DEPENDENT DIELECTRIC PROPERTIES OF Ba-La-Sm-Bi-Ti-O CERAMIC SYSTEM

“…It shows that increase in Bi contents, reduces the variation in dielectric constant with temperature, thereby making the ceramic more temperature stable. This study also reveals that no anomaly was observed in the temperature dependencies of dielectric constant and loss in the temperature range 25 • C-150 • C in both the series, which is in accordance with the earlier work of Belous and co-workers [17,18]. …”

Effects of Temperature Variation on Dielectric Properties of Ba4(La(1 - z)Biz)9.33Ti18O54Solid Solutions

“…No dielectric anomaly was observed for these materials in the temperature range from 298 K to 423 K. It is assumed that there is no structural transition over the temperature range of interest. These investigations are in accordance with the work of Belous et al [14,15]. The dielectric constant varies from 110.40 to 103.96 for z = 0.0 and from 105.87 to 104.57 for z = 0.2 as temperature changes from 298 K to 423 K at 1 MHz.…”

Pseudo-Tungsten Bronze-Type Dielectric Materials

“…Belous et al [55,161,162] studied the temperature dependence of " r and tan for different values of x in Ba 6-x Ln 8 þ 2x Ti 18 O 54 (Ln = La, Nd, Sm, Gd). The studies showed the presence of diffuse anomalies in the temperature dependencies of " r and tan and are below room temperature for La and Nd and above room temperature for Sm-and Gd-based solid solutions.…”

“…Ba 6 Ln 8 Ti 18 O 54 (Ln = La, Pr, Nd, Sm) showed a strongly pronounced maxima in the " r with temperature. It was found [160,162] that the maxima shift toward higher temperatures when the ionic radii of the rare earth element decreased. The diffuse maxima shift as a function of x.…”

“…However, XRD and DSC studies did not indicate any evidence of a structural transition. Belous and Co-workers attributed the observed anomalies to the competition between harmonic and anharmonic contributions of the phonons of the Ba 6-3x Ln 8 þ 2x Ti 18 O 54 crystal lattice, which show an opposite temperature behavior of permittivity and tan [160,162].…”