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Room: 240A
Session Chairpersons: Prof. J.E. Morral, Univ. of Connecticut, 97 N. Eagleville Road, Storrs, CT 06269-3136; Dr. H. Merchant, Gould Electronics, Inc, 35129 Curtis Blvd., Eastlake, OH 44095-4001
2:00 pm INVITED
EXPERIMENTAL AND OPTIMIZED BINARY SYSTEMS OF POST-TRANSITIONAL ELEMENTS: B. Legendre, Y. Feutelais and E. Dichi, Laboratoire de Chimie-Physique Minérale et Bioinorganique, Faculté de Pharmacie, 5 rue J.B. Clément, 92296 Châtenay-Malabry, France
Post transitional elements present a lot of physical properties, especially in the fields of electronic and opto-electronic. Thus the knowledge of binary and ternary phase diagrams is of great importance both for the elaboration of alloys and for their application. One of the characteristics of the elements of post transition is a low melting point and for a large number of them a high vapor pressure. For this last reason it is of great interest to include the gas phase with the condensed phases and to calculate the pressure dependence of the phase diagram. In this lecture, we present experimental data and the result of the optimization for some systems such as: cd-Ge, Cd-Te, Zn-Te, Cd-Zn-Te, Ge-Te, Si-Te, Au-Te. All of these binary systems are included in a database (POSTRANS) compatible with Thermocalc.
2:30 pm
PHASE EQUILIBRIA AND THERMOCHEMISTRY OF THE In-Se SYSTEM: C. Mallika, C.H. Chang, A. Davydov, B.J. Stanbery, T.J. Anderson, Dept. of Chemical Eng., Univ. of Florida, Gainesville, FL 32611
The phase diagram and thermochemistry of the In-Se system have been studied by several investigators, however, the liquid mixture behavior is not well understood. The following galvanic cell: W|In(I),In2O3(s)||In2O3(s),[In]In-Se(s or 1)|C|W was used to determine the activity of In in In-Se liquid alloys in the compositional range 0.10<xse,0.60 and the temperature range 800 to 975 K. Slightly positive deviations from ideal solution behavior were observed in the liquid solution and the measured liquids temperatures were in good agreement with those reported in the literature. In addition, the Gibbs energy of formation for each intermediate compound was derived from the measured values of emf. These results were then combined with other experimental data available in the literature to reassess the thermochemistry and the In-Se phase diagram. Four intermediate solid phases (In4 Se3, InSe, In6Se7, and In2Se3) were considered to be line compounds in this assessment and the Redlich-Kister expression was used to model the liquid phase.
2:50 pm
ASSESSMENT OF THE PHASE DIAGRAM AND THERMODYNAMIC PROPERTIES OF THE As- Ga-Sb AND As-In-Sb SYSTEMS: A. Watson, Univ. of Sheffield, Mappin St., Sheffield S1 3JD, United Kingdom; A. Davydov, S. Misra, T.J. Anderson, Dept. of Chemical Engr., Univ. of Florida, Gainesville, FL 32611
Group III arsenides and antimonides are extremely important materials used in the manufacture of high speed and high frequency electronic devices. In the III-V semiconductor family As-Ga-In-Sb, there are four ternary subsystems. By selecting different compositions within these subsystems, electrical and optical properties of the material can be changed in order to satisfy different applications. In this work, experimental phase diagram information and thermochemical data available in the literature for the As-Ga-Sb and As-In-Sb systems have been critically assessed as a preliminary step towards the study of the As-Ga-In-Sb system. Thermodynamic descriptions of the phases that are consistent with selected experimental data have been produced using the ternary optimizing program TERGSS and thermodynamic descriptions of the binary and unary phases from previous assessments. Phase equilibria and thermodynamic properties are presented which have been calculated from the optimized coefficients using MTDATA. This information can be used for optimizing materials growth conditions and device manufacture.
3:10 pm
POTENTIOMETRIC DETERMINATION OF THE THERMODYNAMIC STABILITY OF SB2O3: R. Lowery, C. Mallika, and T.J. Anderson, Dept. of Chemical Engr., Univ. of Florida, Gainesville, FL 32611
Precise values of thermodynamic properties of Sb2O3 are required to synthesize and characterize the alloys of antimony for applications in thermoelectric devices and semiconductor technology. The Gibbs energy formation of Sb2O3 has been reliably reported in the literature using solid electrolyte emf measurements. This work is extended to determine the phase equilibrium temperatures in Sb/Sb2O3 system. The galvanic cell used in this study can be represented as W|C|Sb(s or 1), Sb2O3(s or 1)_YSZ_ Cu2O,Cu|W. The oxygen potential for the biphasic mixtures were derived from the cell potential data over the temperature range 790 to 983 K. Phase transition temperatures of 845.5 K (Sb2O3, orthorhombic to Sb2O3, cubic), 905.6 K (Sb,s to Sb,1) and 930.0K (Sb2O3,cubic to Sb2O3,1) were obtained from discernible breaks in the emf-T plots. These results agree well with calorimetric values. A value of -712.4 kJ/mol calculated by third-law treatment for DH°f,298 (Sb2O3, orthorhombic) reasonably agrees with literature data.
3:30 pm
PREDICTING OF THE THERMODYNAMIC PROPERTIES FOR THE TERNARY SYSTEM Ga-Sb-Bi: Dragana Zivkovic, Zivan Zivkovic, Univ. of Belgrade, Technical Faculty, 19210, Yugoslavia, Jaroslav Sestak, Czech Acad. of Sciences, Inst. of Physics, 18040 Praha, Czech Republic
Ternary system Ga-Sb-Bi belongs to the group of alloy systems containing semi-conducting compounds, which are important from both the scientific and practical point of view. While binary systems Ga-Sb, Bi-Sb and Ga-Bi are mostly thermodynamically determined, there are only a few data about the thermodynamics of the investigated ternary system Ga-Bi-Sb. Because of the experimental difficulties in thermodynamic determination of this system, connected with the oxidation and volatizing of the present components at investigation temperatures, thermodynamic predicting is applied, and results of the comparative determination of thermodynamic properties in ternary system Ga-Sb-Bi by using following methods: Toop, R-function and general solution model, are given in this paper. Activities, activity coefficients, partial and integral molar quantities for all components in five quasibinary sections of the ternary system Ga-Sb-Bi are determined at temperature 1073K.
3:50 pm
THERMODYNAMIC PROPERTIES AND VAPOR-LIQUID EQUILIBRIUM RELATIONS OF INDIUM-CONTAINING BINARIES: Dajian Wang, Kunming University of Science and Technology, Yunnan, 650093, China
To establish the vapor-liquid equilibrium composition relations of In-Sn, In-Pb, In-Zn, the Miedema's cellular model of heat of formation of binary liquid alloys are employed to correlate the activity coefficients of each component in the binary. Based on the dissimilar Wigner-Seitz atomic cells model, a quantitative analysis of heats of mixing and solution of binary alloys was Miedema. Tanaka deduced the relation between mixing enthalpy and excess entropy of liquid binary alloy. Through the correlation between the heat of formation and excess Gibbs free energy, the activity coefficients and their practical pressures can be analyzed. The obtained results have met the needs of activity coefficients of each component in above alloys in the applications of vacuum separation techniques, as well as in the development of lead-free solder of In-Sn binary or related multicomponent systems.
4:10 pm
APPLICATION OF KNUDSEN EFFUSION MASS SPECTROSCOPY FOR THE STUDY OF THERMODYNAMIC AND PHASE DIAGRAM PROPERTIES OF TRANSITION METAL-TELLURIUM SYSTEMS: M. Sai Baba, Dept. of Chemistry, Texas A&M Univ., College Station, TX 77843; R. Viswanathan, Materials Chemistry Div., Chemical Group, Indira Gandi Centre for Atomic Research, Kalpakkam - 603 102, Tamil Nadu, India
Knudsen effusion mass spectrometric technique has been employed to study the thermodynamic and phase diagram properties of transition metal-tellurium systems. Preferential evaporation of these metal tellurides has been made use of to generate the nonstoichiometric telluride phases in situ. From the variation of tellurium activity as a function of composition, homogeneity ranges of the nonstoichiometric metal tellurides have been arrived at. By applying Gibbs-Duhem integration the thermodynamic activity of the second component could be arrived at. From the activities, partial molar Gibbs free energies were derived. Some of the metal tellerium systems studied include Fe-Te, Cr-Te, Mo-Te and Mn-Te. In this paper we describe some of our results with emphasis on the usefulness of Knudsen effusion mass spectrometric method for deriving such information.
4:30 pm
THE INTERFACIAL REACTIONS IN THE As-Se/Zn COUPLES: Ming-Horng Lin, Sinn-wen Chen, Dept. of Chemical Engr., National Tsing-Hua University, Hsinchu, Taiwan 30043, China; Jinn-lung Wang, Chemical Systems Research Div., Chung-Shan Institute of Science and Technology, Lung-Tan, Taiwan, China
The As-Se-based chalcogenide glasses are IR transparent, and are considered an ideal braze to the ZnSe and ZnS substrates in the IR detector. The interfacial reactions between As-Se and Zn are investigated for fundamental understanding. Three different kinds of reaction couples were prepared, and they were As-50at%Se/Zn at 350°C. As-50at%Se/Zn at 370°C, and As-60at%Se/Zn at 350°C annealed for various length of time. The cross sections of the reaction couples were analyzed by using OM and EPMA. Two phases were formed at the interface, and the diffusion paths were glass/ZnSe/As2Zn3/Zn. The growth rates of the intermetallic layers were also determined by using as image analyzer. The growth rates followed the parabolic law for the type I and type III couples which indicated a diffusion-controlled mechanism.
4:50 pm
THE ATMOSPHERIC OXIDATION OF TELLURIUM: Marc Suys, École Polytechnique de Montréal, Dept. of Chemical Engr, C.P. 6079, centre-ville, Montréal (Québec), Canada DA, H3C 3A7; A. Roy, and J. L'Écuyer, Noranda Advanced Materials, 4950 Lévy, Saint-Laurent (Québec), Canada, H4R 2P1
Tellurium forms technologically important alloys which are being used increasingly in the semiconductor industry (CdTe,Bi2Te3). As such, control of the purity of the source TE metal is critical. Therefore, the understanding of the atmospheric oxidation of tellerium cannot be neglected, as it can be a source of oxygen incorporation in the metal, and thus in the alloys. We have studied, by X-Ray Photoelectron Spectroscopy (XPS), the oxidation of crushed tellerium under various conditions of humidity and air exposure. The rate of oxidation of tellerium is relatively slow: 30 A of tellerium dioxide is detected on the surface of a sample after 8 days of direct air exposure. Our results tend to suggest that the rate-limiting step is the transport of the oxidizing reactant to the tellerium surface. We have also observed that the oxidation reaction is dependent on the relative humidity, as has been reported previously, for thin films, by various authors.
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