Dielectric properties of high-permittivity A2/3CuTa4O12 ceramics

Abstract

Purpose – This paper aims to present the comparative study on the composition, microstructure and dielectric behavior of a group of new nonferroelectric high-permittivity A2/3CuTa4O12 (A = Y, Nd, Sm, Gd, Dy or Bi) ceramics. Design/methodology/approach – The materials under investigation were synthesized by solid-state reaction method and sintered at 1,120-1,230°C. Dielectric properties were investigated in the temperature range from −55 to 740°C at frequencies 10 Hz to 2 MHz. Microstructure, elemental composition and phase composition of the ceramics were examined by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) methods. DC conductivity was studied in the temperature range 20-740°C. Findings – XRD analysis revealed peaks corresponding to Cu2Ta4O12 along with small amounts of secondary phases based on tantalum oxides. Impedance spectroscopic data and the results of SEM and EDS studies imply the spontaneous formation of internal barrier layer capacitors in the investigated materials. Two steps can be distinguished in the dielectric permittivity versus frequency plots. The low-frequency step of 1,000-100,000 is assigned to grain boundary barrier layer effect, while the high-frequency one of 34-46 is related to intrinsic properties of grains. Originality/value – Search for new high-permittivity capacitor materials is important for the progress in miniaturization and integration scale of electronic passive components. The paper reports on processing, microstructure, microanalysis studies and dielectric properties of a group of novel nonferroelectric materials with the perovskite structure of CaCu3Ti4O12 and the general formula A2/3CuTa4O12, being spontaneously formed internal barrier layer capacitors.