title: High-temperature X-ray diffraction and thermal expansion of nanocrystalline and coarse-crystalline acanthite α-Ag2S and argentite β-Ag2S.
abstract: An in situ study of thermal expansion of polymorphic phases of coarse-crystalline and nanocrystalline silver sulfide - monoclinic acanthite α-Ag2S and cubic argentite β-Ag2S - has been carried out for the first time using the high-temperature X-ray diffraction method. The temperature dependencies of the unit cell parameters of acanthite and argentite in the interval of 300-623 K have been determined, and the thermal expansion coefficients of acanthite and argentite have been found. It is shown that the observed difference in the thermal expansion coefficients for nano- and coarse-crystalline acanthite is due to the small particle size of nanocrystalline silver sulfide leading to the growth of anharmonicity of atomic vibrations. It is established by differential thermal analysis that a reversible polymorphic acanthite-argentite phase transformation takes place at ∼449-450 K and the phase transformation enthalpy is equal to ∼3.7-3.9 kJ mol(-1).
authors.affiliation: Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, Ekaterinburg 620990, Russia. gusev@ihim.uran.ru.
authors.forename: S I
authors.initials: SI
authors.lastname: Sadovnikov
authors.affiliation: Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, Ekaterinburg 620990, Russia. gusev@ihim.uran.ru.
authors.forename: A I
authors.initials: AI
authors.lastname: Gusev
authors.affiliation: Ural Federal University named after the First President of Russia B.N. Yeltsin, Ekaterinburg, 620002, Russia.
authors.forename: A V
authors.initials: AV
authors.lastname: Chukin
authors.affiliation: Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, Ekaterinburg 620990, Russia. gusev@ihim.uran.ru.
authors.forename: A A
authors.initials: AA
authors.lastname: Rempel