Microwave dielectric loss in oxides: Theory and experiment

Abstract

We present a model that provides a description of the microwave dielectric loss in oxides. The dielectric loss ͑tan ␦͒ in single crystal and polycrystalline MgO and Al 2 O 3 is measured over the temperature range 70-300 K. We are able to model the dielectric loss in terms of a two-phonon difference model. There are two key parameters in this model: The third derivative, 3 , of the lattice potential and the linewidth, ␥, of the thermal phonons. In polycrystalline samples, rather than considering the different mechanisms of extrinsic loss, it is assumed that the main effect of extrinsic factors is a modification of the linewidth of the thermal phonons. By varying ␥(T), it is shown that the model can describe the loss in both single crystals and polycrystallines materials. In single crystal and polycrystalline MgO, we use ␥ as a fitting parameter. In single crystal and polycrystalline Al 2 O 3 , we obtain ␥(T) by Raman spectroscopy. The theory gives the right order of magnitude of the measured loss.

Temperature and frequency dependence of dielectric loss of Ba(Mg1/3Ta2/3)O3 microwave ceramics

“…The FWHM showed a parabolic variation with the temperature. Aupi et al 6 suggested that such a variation was often found in single crystals. This means that the BMT prepared in this study shows the close characteristics to those of the single crystal.…”

“…First of all, the contribution to the dielectric loss of the two phonon difference process is discussed according to Aupi et al 6 The authors of Ref. 6 suggested that the microwave absorption should simply occur at the BZ boundary, and Eq. (2) was derived as a function of temperature using the theory similar to that of Sparks et al 5 In a more general case, the absorption will occur at the wave vector corresponding to the highest density of states (DOS) of the acoustic phonons; however, it should not affect Eq.…”

“…2, it was found that the dielectric loss had a loss peak at 40 K and gradually increased with temperature in the range of 200-300 K. This peculiar frequency dependence of the dielectric loss is well described by dividing it into two contributions as reported by Zuccaro et al 7 One contribution is a microwave absorption by two phonon difference process and another one is an orientation polarization resonance occurring at the microwave frequency. First of all, the contribution to the dielectric loss of the two phonon difference process is discussed according to Aupi et al 6 The authors of Ref. 6 suggested that the microwave absorption should simply occur at the BZ boundary, and Eq.…”

“…5 Aupi et al investigated the temperature dependence of the dielectric loss of Al 2 O 3 and MgO single crystals. 6 They were successful in analysis of the temperature dependence of dielectric loss and suggested the contribution of acoustic phonons at the BZ boundary.…”

Dielectric properties of magnesium oxide at microwave frequency

“…It is commonly found as a residual phase in the magnesium titanate or magnesium niobate ceramics due to a decomposition of compound or an over-compensated Mg [12][13][14][15]. Studies of the microwave loss of MgO in both polycrystalline and single crystal form have been performed experimentally as a function of temperature up to ∼273 K [16][17][18]. However, the room temperature microwave dielectric properties of simple MgO itself have not been extensively studied.…”