Mn 2+ -Doping Effects on Commensuration and Incommensuration of Ammonium Zinc Chloride Crystal

Abstract

Ammonium zinc chloride (AZC) crystals doped with Mn2+ in different concentrations were grown from aqueous solutions at constant temperature. The dielectric constant (ϵ), dielectric loss (tan δ) and the ac conductivity (σ ac ) along the polar axis were measured as functions of temperature and frequency. The temperature range covered the four high-temperature phases and the measuring frequency extended between 1–100 kHz. The measured properties facilitated the discussion of a model describing formation, annihilation and pinning of the discommensuration in crystal lattice and/or by structural imperfections. The effect of AZC decomposition in the normal phase and the possibility of protonic evolution on the ac conductivity were also considered. The presence of Mn2+ in the position of Zn2+ affected considerably the anomalies detected around the phase transition temperatures of ϵ, tan δ and σ ac . Conduction by translation and/or reorientation hopping are possible in two different frequency ranges depending on the crystal phase character. *On leave of absence from Physics Department, Faculty of Science, Assiut University, 71516 Assiut, Egypt.