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 (10(2)-10(5) 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 Ca1-3/2xYbxTiO3 and CaYbxTi1-xO3 are further driven away from the ferroelectric instability. In contrast, the dielectric properties (10(2)-10(5) Hz) of ceramics corresponding to Ca1-x/2YbxTi1-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.