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Electrical and Thermal Properties of NH 4 Br x CI 1‐ x Single Crystal
Author(s) -
ElKabbany F.,
Tosson M.,
Taha S.
Publication year - 1990
Publication title -
annalen der physik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.009
H-Index - 68
eISSN - 1521-3889
pISSN - 0003-3804
DOI - 10.1002/andp.19905020105
Subject(s) - phase diagram , crystal (programming language) , materials science , differential thermal analysis , phase boundary , ion , analytical chemistry (journal) , atmospheric temperature range , electrical resistivity and conductivity , enthalpy , dielectric , phase transition , phase (matter) , thermodynamics , chemistry , diffraction , physics , optoelectronics , organic chemistry , chromatography , quantum mechanics , computer science , optics , programming language
The effect of partial replacement of Cl − ions by Br − ions in the mixed system of ammonium chloride and ammonium bromide during a set of thermal heating cycles is studied. The study includes electrical measurements (d.c. resistivity, dielectric constant and the spontaneous thermal current), differential thermal analysis (DTA) and dilatometric thermal analysis in the temperature range −60 °C up to 30°C. The results show a large change in the various measured parameters sensitive to thermal agitation process and to the presence of the bromine ions in the mixed crystal system close to the morphotropic boundary x = 0.5. At this boundary the temperature region of the ordered phase extended by about 28°C. The transformation enthalpy was reduced in such case to 41.3 cal/mol. According to the different experimental data of the system NH 4 Br x Cl 1‐ x , a phase diagram was proposed. This phase diagram predicted that the order‐disorder phase transition point changed widely according to the value of x and reached −2°C when the mixed crystal system contained 50% of Br − ions.