Pressure induced structural phase transition inAgSbTe2

Abstract

We report a novel high pressure structural sequence for the functionally graded thermoelectric, narrow band gap semiconductor AgSbTe2, using angle dispersive x-ray diffraction in a diamond anvil cell with synchrotron radiation at room temperature. The compound undergoes a B1 to B2 transition; the transition proceeds through an intermediate amorphous phase found between 17-26 GPa that is quenchable down to ambient conditions. The pressure induced structural transition observed in this compound is the first of its type reported in this ternary cubic family, and it is new for the B1-B2 transition pathway reported to date. Density Functional Theory (DFT) calculations performed for the B1 and B2 phases are in good agreement with the experimental results.PACS numbers: 61.43.Dq, 61.5. Ks, 61.10.Nz, 71.15.Mb Ternary semiconductors with a general formula ABX 2 (A= Cu,Ag ; B=In,Ga,Sb; X= S,Se,Te) with chalcopyrite or rock salt structure are widely used for important technical and device applications. These compounds are found to be excellent candidates for the fabrication of optical frequency converters in solid state laser systems, photovoltaic devices and development of solar cells.1,2,3 While the Cu based chalcopyrites are mainly studied in connection with their photovoltaic applications, the Ag compounds find importance in thermoelectric, optical phase change and frequency conversion applications.4,5 Cubic AgSbTe 2 compounds with Pb doping have been recently shown to be excellent thermoelectric materials with high figures of merit, and are considered promising candidates for future energy production from heat sources.6 AgSbTe 2 with In and V doping undergo, rapid crystalline -amorphous phase transitions on local melting; a property that is used widely to write and rewrite Compact Disks (CD) and Digital Versatile Disks (DVD). 7,8 In comparison with the classical GeSbTe phase change memory alloy, AgVInSbTe is reported to have better erasability and cyclablity in memory switching . 7,8,9,10 The phase changes in these materials are temperature driven, and the previous studies focus mainly on doped thin films of AgSbTe 2 . To our knowledge, no detailed structural reports are available for the host compound AgSbTe 2 , under different temperature or pressure conditions. AgSbTe 2 is isostructural to the rocksalt type II-VI chalcogenides. As the rock salt structure of most of the II-VI compounds is sensitive to pressure, changing from B1 to B2, 11,12 one may expect AgSbTe 2 to display a similar crystallographic transition under pressure. The aim of the present study is to investigate AgSbTe 2 under pressure to explore the structural similarities with its binary analogues. In this paper, we present experimental evidence, for the first time, of a pressure induced structural transition from B1 (crystalline) to B2 (crystalline) with an intermediate amorphous state. This is a new pathway for this structural sequence and is unique in the ABX 2 family. This finding may open up new directions in the search for similar compounds of ...

Athermal amorphization of crystallized chalcogenide glasses and phase-change alloys

“…This is an indication that the bcc phase is richer in Sb and Te and that the remaining amorphous material is Ge-rich. It is interesting to note that the formation of an intermediate amorphous phase during compression has also been observed for AgSbTe 2 [42]. it is informative to start the discussion by looking into the structure of chalcogenide glasses and phase-change alloys.…”

Pressure induced structural transitions in CuSbS2 and CuSbSe2 thermoelectric compounds

“…Many of the ternary chalcogenides undergo pressure-induced structural phase transitions, but the particular pathways vary considerably between the compounds with several ambient crystal structures being a zincblende ( m F43 ) type structure which transform to wurtzite type structure or NaCl type structure [39]. Other compounds, such as AgSbTe 2 , have been found to undergo high-pressure amphorization [9]. A few materials, such as AgInS 2 , crystallize in an orthorhombic structure, but show no indication of a structural phase transition up to 4 GPa at ambient temperature; however, at 400 °C and 2.5 GPa, AgInS 2 undergoes a structural phase transition to a hexagonal α-NaFeO 2 structure [21].…”

“…Many of these compounds display pressure-induced structural phase transitions at varying pressures [9][10][11][12]. Specifically, Cu-based ternary chalcogenide compounds with general formula ABX 2 (A = Cu, B = Sb, X = Te, Se or S) can be regarded as analogues of III -V and II -IV semiconductors and find importance for solar cell and thermoelectric applications [3].…”

“…Specifically, Cu-based ternary chalcogenide compounds with general formula ABX 2 (A = Cu, B = Sb, X = Te, Se or S) can be regarded as analogues of III -V and II -IV semiconductors and find importance for solar cell and thermoelectric applications [3]. These Cubased compounds are analogous to AgSbX 2 compounds, which possess minimal thermal conductivity and as such may exhibit a large dimensionless figure of merit [9,13,14]. CuSbS 2 thin films are promising absorber materials and are used for three dimensional solar cells [15,16].…”

Pressure‐induced structural phase transitions in materials and earth sciences

“…This structure is analogous to the post-rocksalt structure found in zincblende-structured CdTe and ZnTe [59]. Also similar to rocksalt-structured binary compounds, AgSbTe 2 has been found to undergo a transition from the rocksalt towards the CsCl phase [195]. Even though the systematic of phase transitions induced by pressure in chalcopyrites seems to be well established, in the lasts years there was a rebirth of the high-pressure studies on these compounds.…”