Influence of rare earth substitution in Ca0.66Ti0.66R0.34Al0.34O3 (R = La, Sm, Nd) ceramics on crystal structure and microwave dielectric properties

The influence of substitution with rare earth elements in orthorhombic Ca0.66Ti0.66R0.34Al0.34O3 (R = Sm, Nd, La) perovskite ceramics, which were successfully produced with a solid-state reaction method, on their crystal structure (analyzed with Rietveld refinement of X-ray diffractograms and Raman spectroscopy) and on the microwave dielectric properties was investigated. The dielectric constant (εr) increased due to the increase of cell volume, which was a result of the increase of the ionic radius of the rare earth cations incorporated in the host lattice R3+. The values of the quality factors were 43620.74, 41292.71, and 38389.57 GHz for the Sm-, Nd-, and La-containing ceramics, respectively. The decrease of these values is correlated to the level of distortion of the octahedral due to the incorporation of the three different rare earth cations. The temperature coefficient of resonant frequency increased from 4.99 for the Sm-ceramics to 9.92 ppm/°C for the La-ceramics, attributed to the increase of cell polarization.