Conductivity studies of some diphosphates with the general formula AI2BIIP2O7 by impedance spectroscopy

The conductivity mechanism of three crystalline diphosphates of (AI2BIIP2O7) type, Na2CaP2O7, Na2CuP2O7 and K2MnP2O7 has been investigated using combined complex impedance and modulus formalisms. Their conductivity measurements showed that Na2CaP2O7 and Na2CuP2O7 can be considered as pure ionic conductors, while K2MnP2O7 is a mixed ionic-electronic conductor with a relatively electronic nature. In the case of K2MnP2O7, the electron transport, originated from the electronic hopping, is due to the presence of various oxidation states of the manganese ion. The conductivity measurements of the diphosphate compounds have been carried out using the frequency range between 10−1 and 106 Hz over a temperature interval from 300 to 700 K. The equivalent circuit, which provides the most realistic model of the electrical properties of each compound under investigation, was studied using the least squares immittance fitting program (LEVEM). A correlation between electrical and structural properties of the diphosphates has been conducted.