Dielectric response in the charge-ordered Ca2−xPrxMnO4 phases

We have prepared Ca2−xPrxMnO4 (x=0,0.25,0.33 and 0.50) compounds by the so-called “liquid-mix” method. X-ray powder diffraction indicated that these compounds are single-phase materials and resistivity measurements showed that the Pr-doped samples experience charge-ordering (CO) transitions at 275 K (x=0.25), 330 K (x=0.33) and 315 K (x=0.50). The intrinsic dielectric constants calculated by impedance spectroscopy (IS) from the values of the obtained bulk capacitances were remarkably high: 217, 37 and 80 for the x=0.25,0.33 and 0.50 samples, respectively. In addition, extrinsic factors play an important role on their dielectric response, especially at T>150K, giving rise to very high dielectric constants at room temperature (ɛr′∼106). Also, and for comparison, we have studied the dielectric response of Ca2MnO4 (non charge-ordered compound), finding much smaller dielectric constant values and an intrinsic contribution ɛr′(bulk)=14, remarkably lower than in the case of Pr-doped compounds. These results could be a new evidence of the link between the charge ordered state and the increase of the dielectric constant.