Mg2MTaO6 (M=Nd or La): a group of new pyrochlore oxides

Influence of A-site Cation on Structure and Dielectric Properties in A2DyBiO6 (A=Mg, Ca, Sr, Ba) Double Perovskites

“…The strongest reflection peak at a 2y value of around 308 identified in Ca 2 DyBiO 6 and Sr 2 DyBiO 6 samples are assigned to (1 1 2). Mg 2 DyBiO 6 double perovskite is indexed as a defective cubic pyrochlore structure with a Fd-3m space group, [20] while Ba 2 DyBiO 6 double perovskite crystallised in cubic system has a Fm-3m space group. [11] Unfortunately, the existence of a secondary phase can be observed for the Mg and Ba samples and this was identified as Bi 2 O 3 (cubic system, COD1010313), according to the diffraction peak at 2y ¼ 27.38.…”

“…At high frequencies, the dielectric constant becomes independent of frequency, as reported by Laishram et al, [23] because the dipoles can no longer follow the field. The experimental data indicate that by changing A from Ca to Sr and Ba the permittivity increases, which may be related to the decrease in concentration of dipoles [20] due to the increase in unit-cell volume.…”

“…According to the experimental range of frequencies reported in the literature, the dielectric constant (e 0 ) of these defective pyrochlore materials is predominantly determined by the contribution of ionic polarisation. [20] In other double perovskite structure-containing samples, the dipole follows the field at low frequencies, but as the frequency increases, the dipoles start lagging behind the field and the real part (e 0 ) of the dielectric constant decreases. At high frequencies, the dielectric constant becomes independent of frequency, as reported by Laishram et al, [23] because the dipoles can no longer follow the field.…”