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Ag 5 Te 2 Cl 1− x Br x ( x = 0 – 0.65) and Ag 5 Te 2− y S y Cl ( y = 0 – 0.3): Variation of Physical Properties in Silver(I) Chalcogenide Halides
Author(s) -
Nilges Tom,
Lange Stefan
Publication year - 2005
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.200500261
Subject(s) - tetragonal crystal system , monoclinic crystal system , chalcogenide , halide , crystallography , analytical chemistry (journal) , materials science , differential thermal analysis , phase transition , ion , crystal structure , chemistry , inorganic chemistry , diffraction , thermodynamics , optics , physics , organic chemistry , chromatography , metallurgy
The structures, thermal and physical properties of ion conducting polymorphic Ag 5 Te 2 Cl 1− x Br x and Ag 5 Te 2− y S y Cl have been investigated. A maximum substitution degree of x = 0.65 and y = 0.3 was derived from X‐ray powder diffraction. Mixtures of silver halides, silver chalcogenides and Ag 3 TeBr were observed for higher substitution degrees. Both silver chalcogenide halide systems show a Vegard type behaviour. Single crystal structure determinations of selected materials were performed at different temperatures to analyse the silver distribution in the tetragonal high temperature α ‐ and the monoclinic room temperature β ‐phases. After non‐harmonic refinement of the silver positions detailed joint probability density function analysis ( jpdf ) and determination of one particle potentials ( opp ) were carried out to investigate the diffusion pathways and bottlenecks of ion transport for those materials. A preferred anisotropic ion transport along the $^{1}_{\infty}\rm [AG]$ diffusion pathways for the α ‐ and 1D zig‐zag diffusion pathways for the β ‐phases were found. α – β and β ‐ γ phase transitions were determined by DSC and DTA methods and conductivities were measured using temperature dependent impedance spectroscopy. The substitution of tellurium by sulphur lowered the α – β phase transition from 334 K (Ag 5 Te 2 Cl) to 270 K (Ag 5 Te 1.8 S 0.2 Cl) while the opposite trend was found for the Ag 5 Te 2 Cl 1− x Br x phases. The α – β phase transition of Ag 5 Te 2 Cl 0.35 Br 0.65 at 343 K represents the highest transition observed for the silver chalcogenide halides under discussion. Total conductivities of approx. 1 Ω −1 cm −1 ( α ‐Ag 5 Te 2 Cl 0.5 Br 0.5 ) and 0.24 Ω −1 cm −1 ( α ‐Ag 5 Te 1.8 S 0.2 Cl) at 473 K were found being slightly higher (Br) and lower (S) than the conductivity observed for α ‐Ag 5 Te 2 Cl. A conductivity jump of more than two orders of magnitude, related to the α – β phase transitions, within the temperature range from 270 to 343 K is adjustable by simple variation of the composition and is therefore an extraordinary feature of these materials. The total conductivity is linearly correlated to the volume of the anion substructure and can be varied within more than half an order of magnitude.