Defect chemistry and dielectric properties of Yb3+:CaTiO3 perovskite.

The defect chemistry of Yb³⁺:CaTiO₃ solid solutions has been investigated both theoretically and experimentally. Three different incorporation mechanisms with similar solution energy were predicted for Yb³⁺ by atomistic simulation: (i) Ca site substitution with Ca vacancy compensation; (ii) Ti site substitution with O vacancy compensation; (iii) simultaneous substitution at both Ca and Ti sites with self-compensation. X-ray diffraction and scanning electron microscopy results strongly support the possibility to realize the above defect chemistries in CaTiO₃ by changing the Ca/Ti ratio to force Yb³⁺ on the Ca site (Ca/Ti<1), on Ti site (Ca/Ti>1), or on both sites (Ca/Ti=1) according to the calculations. The temperature dependence of the relative dielectric constant (10²–10⁵ Hz) of ceramics corresponding to predominant Yb substitution either at the Ca site or the Ti site is qualitatively similar to that of undoped CaTiO₃. The Curie-Weiss temperature is shifted to more negative values in comparison to CaTiO₃, suggesting that the compositions Ca_1-3/2xYb_xTiO₃ and CaYb_xTi_1-xO₃ are further driven away from the ferroelectric instability. In contrast, the dielectric properties (10²–10⁵ Hz) of ceramics corresponding to Ca_1-x/2Yb_xTi_1-x/2O₃ are radically different. The relative dielectric constant is increased of about one order of magnitude (2200 at 30 K), is almost independent of temperature, with a maximum variation of 20% in range of 20–300 K, and shows frequency dispersion above 150 K. The loss tangent at 20–300 K is <5% for frequencies >=1 kHz. The possible mechanism for the observed dielectric behavior is discussed. [ABSTRACT FROM AUTHOR]