Characterization of structure and properties in CaO-Nd2O3-TiO2 microwave dielectric ceramic modified by Al2O3

Abstract

The structure and properties of Ca0.61Nd0.26Ti1-xAlxO3 (0 ≤ x ≤ 0.05) ceramics are explored by using XRD, SEM, Raman spectrometer, TEM, XPS, etc. All compositions are formed the main phase with orthorhombic perovskite structure, whereas the second phase TiO2 exists in the range of x = 0.02–0.05. The Rietveld refinement results show that the lattice parameters and the unit cell volume decrease as x value increases, and the εr and τf values decline. The Raman spectra prove that the Ag(3) mode related to the TiO bending is blunted, owing to the increasing average lattice energy values of Ti/Al-O bond. This result implies the oxygen octahedral structure becomes more stable with increasing content of Al3+, which is in favor of the decline of the positive τf values for Ca0.61Nd0.26Ti1-xAlxO3 samples. The generation of Ti3+ has been restrained when x = 0.01, which is confirmed by XPS results. Meanwhile, the 1:1 ordered areas are detected in sample at x = 0.05 by HRTEM, and the corresponding SAED patterns present faint spots among the bright diffraction spots, indicating the super-lattice structure. Consequently, the Q × f value dramatically increases from 11,356 GHz at x = 0 to 18,128 GHz at x = 0.05 for Ca0.61Nd0.26Ti1-xAlxO3 samples.