Separation of surface and bulk electrical conductivity in KH2PO4 and KH2AsO4 crystals at high temperatures

The electrical conductivity measurements on single crystals of KH2PO4 and KH2AsO4 have been carried out in the temperature range from room temperature to 200 °C. The value of kBTε″ showed a high-temperature anomaly around Tp (182 °C for the KH2PO4 and 180 °C for the KH2AsO4). The total activation energies are obtained Et=0.42 in KH2PO4 and Et=0.40 in KH2AsO4 for the ionic conduction of mobile ions, including bulk and surface conduction. From complex ac impedance spectra, we observed the impedance consisting of two regions for measuring frequency: the high frequency region may be due to proton migration in the bulk, while the low frequency region may be due to charge transport at the surface. We separated bulk conductivity by means of complex impedance formalism. The bulk activation energies are obtained EB=0.68 eV in KH2PO4 and EB=0.59 eV in KH2AsO4.