Correlation Between Tolerance Factor and Temperature Coefficient of Dielectric Constant of (Ba,Sr)(Zn1/3Ta2/3)O3 Dielectric Resonator

Abstract: Theory and experimental results are presented to show the possibility of using a resonant post technique for characterizing dielectric and magnetic materials at microwave frequencies. Results of the temperature dependence of the relative dielectric constant of nonmagnetic materials with /spl epsilon//sub r/, varying from 4 to 60 are presented and also loss tangent measurements at room temperature. The complex permittivity and permeability of a number of garnet materials has also been measured with 4/spl pi//spl gamma/M/sub s/ / /spl omega/ varying from 0.25 to 0.8. The measured real part of the permeability is in good agreement with the theoretical predictions of Schlomann and the imaginary part of the permeability agrees with measurements by Green et al. on similar materials.

Abstract: The temperature coefficient of the dielectric permittivity (τe) of nonferroelectric complex perovskites is of importance in the application of these cermaics to microwave filters and resonators. Recent work has directly related changes in the τe of complex perovskites to the onset of structural phase transitions which involve tilting of the octahedra. It can be argued that the onset of octahedral tilting is controlled by the tolerance factor (t). Thus, a relationship between τe and t is postulated. This relationship is discussed and transmission electron microscopy is used to demonstrate examples of the structural modifications which cause the anomalies in τe at given values of t.

Abstract: The dielectric properties at microwave frequencies of Ba(Zn1/3Ta2/3)O3 ceramics prepared by sintering were investigated. These ceramics had lower density but higher loss quality than ceramics hot-pressed at 1400°C. Loss quality was greatly improved by prolonged sintering. The Q of the ceramics measured by the dielectric resonator method was 14 000 at 12 GHz. The ceramics were investigated by X-ray diffraction analysis. It was found that Q improvement corresponds with increased Zn and Ta ordered structures in the ceramics.

Abstract: The temperature and pressure dependence of the dielectric constant of a number of cubic halides and oxides with a broad range of dielectric constants have been determined. For low-$\ensuremath{\epsilon}$ compounds the dielectric constant increases with increasing temperature, whereas for high-$\ensuremath{\epsilon}$ compounds the dielectric constant decreases with increasing temperature. Hydrostatic pressure lowers the value of the dielectric constant for all compounds measured. For ferroelectrics and antiferroelectrics a relation has been found between the Curie temperature and the Curie constant. Three effects contribute to the temperature dependence of a dielectric constant: the decrease in the number of polarizable particles per unit volume as the temperature increases, which is a direct result of the volume expansion ($A$), the increase of the macroscopic polarizability due to the volume expansion ($B$), and the temperature dependence of the macroscopic polarizability at constant volume ($C$). The experimental data have been used to calculate these different contributions. It is found that the volume-dependent contribution ($A+B$) is always positive and that the direct temperature contribution ($C$) can be either positive or negative. Where optical data were available in literature they were used to calculate the contributions of the optical and infrared parts of the polarizability to the temperature and volume dependence of the polarizability. The results are discussed with the use of a classical ionic model.