Dielectric Properties Of MRAlO₄ Type Oxide Ceramics At Low Frequency

In recent years, with the development of microwave applications, microwave dielectric ceramics with high dielectric constant play an important role' in the miniaturization of microwave components.These materials have receiving increasing scientific and commercial interests. The MRAlO₄ ?M = Ca and Sr; R = La, Nd, Sm, and Y? layered compounds with the K2NiF4-type structure, such as CaNdAlO₄ and SrLaAlO₄, exhibit suitable lattice parameters for strain engineering and excellentthermal expansion matching with many functional materials. Therefore, they have been widely used as important substrate materials for preparation thin films of high-temperature superconducting, ferroelectric, magnetic, and multiferroic materials.Among the MRAIO4 family, calcium lanthanum aluminum oxide ?CaLaAlO₄? and strontium lanthanum aluminum oxide ?SrLaAlO₄? have been proved to be promising microwave dielectric ceramic material because they all show good microwave dielectric properties. As a result, the application prospect is very broad.It was reported that the extrinsic loss part resulting from the interfacial effects, caused by such as porosities, secondary phases, and grain boundaries, strongly affects the microwave dielectric properties. To eliminate the extrinsic loss part, the full knowledge of the dielectric properties related to the interfacial effects of CaLaAlO₄ andSrLaAlO₄ is of vital important. Unfortunately, the existing reports were mainly measured on microwave frequency range. In such a high frequency range, the dielectric polarization of interfacial effects known as Maxwell-Wagner polarization cannot follow the variations of the applied field and hence the interfacial effects cannot be characterized by these measurements. In this paper, We present detailed investigations on the low-frequency ?20 Hz-10 MHz? dielectric properties of CaLaAlO₄ and SrLaAlO₄,which were prepared via solid state reaction method in a wide temperature range from room temperature ?RM? to 700?, and get the following results:?1? We found that the CaLaAlO₄ sample has a larger dielectric constant of ?20 and a smaller dielectric loss at less than 100 ?. And at this time the sample primarily has an intrinsic dielectric response dominated by electron or ion polarization. As the temperature increases, it is observed that CaLaAlO₄ has a giant dielectric behavior similar to that of CaCu3Ti4O12,and it consists of two thermally activated dielectric relaxations. The low-temperature relaxation is caused by the bulk response related to the hopping motion of oxygen vacancies, and the high-temperature one is an interfacial relaxation due to grain boundaries. Our results revealed that the giant dielectric behavior is mainly caused by the interfacial relaxation.?2? It was found that SrLaAlO₄ shows intrinsic dielectric behavior with a dielectric constant of 13 in the temperature range below -300?. In the temperature range of 300 to 560 ?,the bulk dielectric contribution of the oxygen-vacancy-related polarons dominates the dielectric properties of the sample. Whereas,the dielectric properties is controlled by the sample/electrode contacts in the temperature range above 560 ?. Our results indicate that the bulk effect instead of interfacial effect is the main contribution of dielectric loss in the lower temperature range.