Polaron conductivity mechanism in potassium acid phthalate crystal: AC-conductivity investigation

Abstract

The complex dielectric constant, , of potassium acid phthalate monocrystal (KAP) was investigated over the broad frequency and temperature range. While the imaginary part of dielectric constant ε′′(ν) increases rapidly with increasing temperature in the studied temperature range, the real part of dielectric constant ε′(ν) increases only at high temperatures; there is almost no change of ε′(ν) below 200 K. Both values of ε′ and ε′′ are frequency dependent; the values increase with decreasing frequencies. At temperatures below 450 K the ac electrical conductivity and dielectric constant follow simultaneously the universal dielectric response (UDR). The analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for small polarons revealed that this mechanism governs the charge transport in KAP crystal in the studied temperature range.

Lateral deformations of a crystal of potassium acid phthalate in an external electric field

“…The weakest bond is ionic (K-O) (Kong et al, 2010;Nelyubina et al, 2008); therefore, potassium ions K + can act as the main charge carriers in a certain temperature range. Filipič et al (2016) The asymmetric unit in the KAP structure.…”

“…Despite the large number of reports devoted to the study of the physical properties of KAP crystals, the dielectric and conductive properties have not been studied so actively. Noteworthy are the studies by Varma et al (1988), Kejalakshmy & Srinivasan (2003), Bott et al (2009) and Filipič et al (2016), as well as studies of KAP crystals doped with bivalent strontium (Sajikumar et al, 2015) and trivalent iron and chromium (Kejalakshmy & Srinivasan, 2004). The mechanism of conductivity of these crystals is not well understood.…”

“…There is a strongly asymmetric onedimensional single-well potential for the proton, which indicates a strong anharmonicity of the antisymmetric stretching vibration of OHO (Derzsi & Colognesi, 2010;Bott et al, 2009). Other researchers (Filipič et al, 2016) believe that the main charge carriers in the temperature range 5-450 K are small polarons (the radius is less than the lattice constants). They are formed in spiral chains of ortho-phthalic acid molecules as a result of the transfer of a proton from acid molecules to water molecules along hydrogen bonds.…”