Experimental Investigation and Thermodynamic Calculations of the Bi-Ge-Sb Phase Diagram
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UCTION
THE Ge-Sb–based systems have attracted considerable attention over the last few decades[1–5] due to their potential application as a new type of memory that is based on crystalline-to-amorphous state phase transition, i.e., phase-change material (PCM). In order to be considered as a potential PCM, alloys should possess good thermal stability and fast crystallization ability and be devoid of segregation of phases after the record/ erase cycle. Consequently, there are only a limited number of PCMs that have any practical applications.[6] Ge-based alloys have wide industrial applications and can be found in optical discs, DVDs, Blue-Ray discs, and flash memory devices,[7] as well as in different optical and electronic devices, transistors, optical cables, semiconductors, integrated circuits, etc.[8–17] The aim of this study is the experimental and computational investigation of phase transitions and microstructures of alloys in the ternary Bi-Ge-Sb system. Selected alloys of the Bi-Ge-Sb ternary system were prepared and studied using a combination of different experimental techniques (differential thermal analysis (DTA), scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), and X-ray diffraction MILENA PREMOVIC´, Assistant, and DUSˇKO MINIC´, Full Professor, are with the Faculty of Technical Science, University in Prisˇ tina, Kosovska Mitrovica, Serbia. Contact e-mail: dminic65@ open.telekom.rs VLADAN C´OSOVIC´, Senior Research Associate, is with the Institute of Chemistry, Technology and Metallurgy, University of Belgrade, Belgrade, Serbia. DRAGAN MANASIJEVIC´, Assistant Professor, and DRAGANA ZˇIVKOVIC´, Full Professor, are with the Technical Faculty, University of Belgrade, Bor, Serbia. Manuscript submitted February 3, 2014. Article published online July 18, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
(XRD)). Experimentally obtained results were compared with predicted phase equilibria. In addition, Brinell hardness of the alloys from three vertical sections of the ternary Bi-Ge-Sb system was studied. The obtained results presented in this study should contribute to further development of this application area, especially considering that the literature data related to this system are scarce. II.
EXPERIMENTAL PROCEDURE
All investigated samples were prepared from Bi, Ge, and Sb shots of 99.99 at. pct purity in an induction furnace under high-purity argon atmosphere. Given that Sb is highly volatile, before melting, an additional amount of Sb (about 1 to 3 at. pct) was added to compensate for the weight loss. The phase transformation temperatures were determined by the DTA method using a TA Instruments SDT Q600 (New Castle, DE). The samples weighing between 10 and 15 mg were placed in alumina crucibles and analyzed at a heating rate of 5 K (5 C)/min. The sample masses and heating rates were determined by analysis of one sample under different testing conditions. The measurements were carried out under flowing nitrogen atmosphere with an empty alumina crucible as reference material. The equilib
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