Mn2+doping-induced-effects on commensuration and incommensuration of potassium zinc chloride crystal

Abstract

Undoped and Mn2+-doped with different concentrations of potassium zinc chloride (KZC) crystals were grown from aqueous solutions by slow evaporation. The dielectric constant (ε), dielectric losses (tan δ) and ac conductivity (σac) of the crystals in the ferroelectric-commensurate, incommensurate and normal phases have been measured as a function of frequency, in the range 1–100 kHz, and temperature, in the range 300–580 K. Virgin samples were subjected to measurements of the frequency dependence at selected temperatures and measurements of the temperature dependence was then followed using the same samples. The increase of ε with T could be due to a combination of conductivity, structural variations and discommensuration (DC) formation and pinning as well. The increase of tan δ with temperature was attributed to relaxation loss in addition to conduction loss, which increases more rapidly with temperature. The ac conductivity (σac) and tan δ along the polar axis of KZC increased significantly with increasing Mn2+ content while ε decreased. σac changed with frequency according to a power law of the form σac = f s where 0.15<s<1.27. A linear decrease of ε and tan δ with increasing the frequency was also found. The obtained results were treated by considering the effect of Mn2+-doping on stripples nucleation, DC evolution/annihilation, DC-lattice formation and DCs pinning by the crystal lattice and/or structural defects for virgin and thermally treated samples.