Crystal chemistry of natural tellurides II: Redetermination of the crystal structure of krennerite, (Au1−x Ag x ) Te2 withx∼0.2 (original) (raw)

Summary

The crystal structure redetermination of krennerite (_a_=16.58,_b_=8.849,_c_=4.464 Å;Z_=8; space group:Pma_2-C /42_v ) with 1063 X-ray data yielded an_R_-value of 5.8%. Within the structure, there are three crystallographically different noble metal positions. Two of them are statistically occupied by Au and Ag atoms (ratios of 75∶25 and 50∶50, respectively) and one position by Au atoms only. The (Au, Ag) atoms are surrounded by six Te atoms with a [2+2+2] coordination. The Au atom has a [4+2] coordination built up by six Te atoms. These three different coordination polyhedra are linked via common Te−Te edges to rugged “sheets” parallel to (010). These “sheets” are connected to a framework by four crystallographically different Te atoms—combined to one Te3 group and two Te2 dumb bells (with Te−Te<2.9 Å). A fifth Te atom is only surrounded by (Au, Ag) and Au atoms. According to these different structural elements the crystal chemical formula may be written as (Au2−_x Ag x )Au2[Te3][Te2]2[Te];_x_∼0.8.

Zusammenfassung

Die Kristallstruktur des Minerals Krennerit (_a_=16,58,_b_=8,849,_c_=4.464 Å;Z_=8; Raumgruppe:Pma_2-C /42_v ) wurde neu bestimmt. Die Strukturverfeinerung ergab mit 1063 Röntgenintensitäten_R_=5,8%. In dieser Struktur gibt es drei kristallographisch verschiedene Edelmetallpositionen. Zwei davon sind statistisch mit Au- und Ag-Atomen (Verhältnis 75∶25 bzw. 50∶50), eine nur mit Au-Atomen besetzt. Die (Au, Ag)-Atome werden von sechs Te-Atomen in einer [2+2+2]-Koordination umgeben, das Au-Atom besitzt eine [4+2]-Koordination von sechs Te-Atomen. Diese drei verschiedenen Koordinationspolyeder werden über gemeinsame Te−Te-Kanten zu gewellten “Schichten” parallel (010) verbunden. Durch vier kristallographisch verschiedene Te-Atome-die ihrerseits zu einer Te3-Gruppe und zwei Te2-Hanteln (mit jeweils Te−Te<2.9 Å) verbunden sind—werden diese “Schichten” zu einem Gerüst verknüpft. Ein fünftes Te-Atom wird nur von (Au, Ag)-bzw. Au-Atomen umgeben. Entsprechend diesen verschiedenen Bauelementen kann die kristallchemische Formel wie folgt geschrieben werden. (Au2−_x Ag x )Au2[Te3][Te2]2[Te];_x_∼0,8.

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1. F. Pertlik
   Present address: Institut für Mineralogie und Kristallographie der Universität Wien, Dr. Karl Lueger-Ring 1, A-1010, Wien, Austria

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Pertlik, F. Crystal chemistry of natural tellurides II: Redetermination of the crystal structure of krennerite, (Au1−x Ag x ) Te2 with_x_∼0.2.TMPM Tschermaks Petr. Mitt. 33, 253–262 (1984). https://doi.org/10.1007/BF01082672

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• Received: 26 March 1984
• Accepted: 18 May 1984
• Issue Date: December 1984
• DOI: https://doi.org/10.1007/BF01082672

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