Dielectric properties of RE2W2O9 (REÂ =Â Pr, Sm-Gd) ceramics

The UV-vis-NIR and electrical conductivity σ(T) measurements of RE2W2O9 (RE = Pr, Sm-Gd) showed the insulating state and the calculated value of the direct allowed energy gap Eg > 3.5 eV. Thermoelectric power S(T) measurements showed the n-type conduction for Sm2W2O9 and Eu2W2O9 as well as p-type one for Pr2W2O9 and for Gd2W2O9. The I-V characteristics, measured at 300 and 400 K, showed the symmetrical and linear behaviour of electron emission, slightly higher at higher temperature. Relative dielectric permittivity ɛr as well as loss tangent (tan δ) do not depend both on the temperature in the range of 76-400 K and the frequency in the range of 5 × 102-1 × 106 Hz. ɛr increases from 8 via 11 and 18 to 33 in the sequence: Gd, Eu, Pr and Sm, respectively. Since the loss factor is close to zero (tan δ < 0.005), the test materials can be considered a dielectric (with energy storage potential).