Фазовая диаграмма системы Ge-Se

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Ge-Se (Germanium-Selenium) A.B. Gokhale and G.J. Abbaschian The assessed Ge-Se phase diagram is based primarily on the work of [82Ips], with review of the experimental data of [62Liu], [65Dem], [68Kar], [68Vin], [ 69Ros], [72Que], and [84Gla]. [82Ips] is considered to be the most reliable source because of the thoroughness of the investigation and the wide range of compositions investigated. The system is characterized by a monotectic at 904 C and ~11.5 at.% Se, with the limit of liquid immiscibility extending to 40 at.% Se; a nearly stoichiometric intermediate phase, GeSe, which forms peritectically at 675 C and transforms polymorphically from cubic to a low- temperature orthorhombic structure between 666 and 647 C; a stoichiometric intermediate phase, GeSe2, with a monoclinic structure and congruent melting point at 742 C; and a eutectic between aGeSe and GeSe2 at 583 C and a 56 at.% Se, and another between GeSe2 and (Se) at 212 C and 92 at.% Se. The eutectic between GeSe2 and (Se) is indicated at 92 at.% Se based on the data of [65Dem] and [68Vin] instead of the 94.5 at.% Se composition of [82Ips]. [82Ips] noted that because of its steepness, the GeSe2 liquidus on the Se- rich side could not be determined accurately. Consequently, the extrapolation of their liquidus to the eutectic isotherm may be somewhat inaccurate. Furthermore, the data of [65Dem] and [68Vin] are supported by the observation that the 92 at.% Se composition exhibits a very strong tendency towards glass formation [76Pol, 78Esq]. The liquidus is reliably established except for the boundaries of the miscibility gap. According to [69Ros], the miscibility gap boundaries could not be determined due to very weak thermal effects associated with liquid separation. Based on the Hall coefficient measurements as a function of temperature, [ 59Tyl] indicted the solubility of Se in (Ge) to be retrograde and on the order of 1.13 x 10-8 at.%. The solubility of Ge in (Se) has not been measured, but is likely to be very small. GeSe transforms allotropically from cubic to a low-temperature orthorhombic modification. [82Ips] indicated the allotropic transformations at 666 с 4 C and 647 с 4 C on the Ge-rich and Se-rich sides, respectively. The latter, however, speculatively included a small (0.5 at.% Se) compositional difference between a and b forms, with a decomposition of bGeSe through an inverse peritectic reaction. In this evaluation, a homogeneity range of 0.5 at.% is indicated for GeSe following [68Kar]. The P-T-X equilibria in Ge-Se were determined by [70Kar] using the quartz null- manometer diaphragm method. [70Kar] determined the total pressure, with a claimed accuracy of с1 mm Hg as a function of temperature for the S-L-G three- phase equilibria in the range 20 to 70 at.% Se. Se-rich Ge-Se alloys show a strong tendency towards glass formation. The most common methods of preparing amorphous alloys appear to be thermal sputtering on unheated substrates or quenching liquid alloys in ice-water mixture. Substrates heated to 300 C have been reported to lead to a crystalline matrix [70Gos]. The glass transition temperature (Tg) of the amorphous alloys increases monotonically from approximately 40 to 400 C with increasing Ge content in the range 0 to 33 at.% Ge [65Dem, 76Ber, 77Bor, 78Esq]. [77Bor] also measured the crystallization temperatures (Tr) of amorphous Ge-Se alloys. Their data indicated a monotectic increase in Tr from86 to 490 C in the range 0 to 33 at. % Ge. [77Bor] did not detect a Tr for the Ge-90 at.% Se alloy; this composition, close to the eutectic at 92 at.% Se, apparently transforms from the amorphous state directly into liquid without intermediate crystallization. According to [76Pol], the short-range order in amorphous Ge0.09Se0.91 is essentially the same as that of its liquid. According to [65Dem] and [78Esq], the eutectic composition (92 at.% Se) is the most stable glass former. Upon crystallization, the conductivity of amorphous GeSe was reported to increase irreversibly by a factor of 2 to 3 [72Zak]. The short-range order in amorphous Ge-Se alloys has been deducted from radial distribution functions derived by Fourier transformation of diffraction data [ 72Faw, 73Pol, 74Mol, 74Uem, 76Pol]. The results indicated a monotonic increase in the coordination number (CN) from 2.4 (Se) to 4.0 (Ge). [72Faw] explained the results on the basis of a random covalent bond model assuming that the local valence requirements are satisfied in the whole composition range. [ 74Uem] additionally found a singularity in CN at 33 at.% Ge, indicating a similarity in the short-range order of amorphous and crystalline GeSe2. In contrast, the amorphous structure of GeSe is considerably distorted with respect to its crystalline counterpart [73Pol, 74Uem]. [80Kaw] indicated a monotonic increase in the band gap of amorphous alloys in the range 0 to 33 at.% Ge, with a maximum of ~5 eV at GeSe2; the band gap decreases sharply between 40 and 50 at.% Se. 59Tyl: W.W. Tyler, J. Phys. Chem. Solids, 8, 59-65 (1959). 62Liu: C.H. Liu, A.S. Pashinkin, and A.V. Novoselova, Proc. Akad. Sci. USSR, Chem. Sect., 146, 892-893 (1962). 65Dem: S.A. Dembovskii, G.Z. Vinogradova, and A.S. Pashhinkin, Russ. J. Inorganic Chem., 10(7), 903-905 (1965). 65Dut: S.N. Dutta and G.A. Jeffrey, Inorganic Chem., 4(9), 1363-1366 (1965). 68Kar: S.G. Karbanov, V.P. Zlomanov, and A.V. Novoselova, Vestn. Mosk. Univ. Khim., 23(3), 96-98 (1968). 68Vin: G.Z. Vinogradova, S.A. Dembovskii, and N.B. Sivkova, Russ. J. Inorganic Chem., 13(7), 1051-1052 (1968). 69Ros: L. Ross and M. Bourgon, Can. J. Chem., 47(14), 2555-2559 (1969). 70Gos: A. Goswami and P.S. Nikam, Indian J. Pure Appl. Phys., 8, 798-800 (1970) . 70Kar: S.G. Karbanov, V.P. Zlomanov, and A.V. Novoselova, Vestn. Mosk. Univ. Khim., 11(1), 51-55 (1970). 72Faw: R.W. Fawcett, C.N.J. Wagner, and G.S. Cargill, J. Non-Cryst. Solids, 8- 10, 369-375 (1972). 72Que: P. Quenez, P. Khadadad, and R. Ceolin, Bull. Soc. Chim. Fr., 1, 117-120 (1972) in French. 72Zak: V.P. Zakharov and V.I. Zaliva, Kristallografiya, 17(1), 198-202 (1972) in Russian; TR: Sov. Phys. Crystallogr., 17(1), 161-164 (1972). 73Pol: Yu.G. Poltavtsev and V.P. Zakharov, Sov. Phys. Crystallogr., 18(3), 379- 380 (1973). 74Mol: B.J. Molnar and D.B. Dove, J. Non-Cryst. Solids, 16, 149-160 (1974). 74Uem: O. Uermura, Y. Sagara, and T. Satow, Phys. Status Solidi (a), 26, 99- 103 (1974). 75Wie: H. Wiedemeier and P.A. Siemers, Z. Anorg. Allg. Chem., 411, 90-96 (1975) . 76Ber: J.S. Berkes, J. Non-Cryst. Solids, 18, 405-410 (1976). 76Dit: G. Dittmar and H. Schafer, Acta Crystallogr. B, 32, 2726-2728 (1976). 76Pol: Yu.G. Poltavtsev and V.M. Pozldnyakova, Zh. Fiz. Khim., 49, 1556-1558 ( 1975) in Russian; TR: Russ. J. Phys. Chem., 49(6), 918-920 (1975). 77Bor: S. Bordas, N. Claraguera, M.D. Baro, M.T. Claraguera-Mora, and J. Casas- Vazquez, Therm. Anal. Proc. Int. Conf., 5th, H. Chihara, Ed., 14-17 (1977). 78Esq: M. Esquerre, J.C. Carballes, J.P. Audiere, and C. Mazieres, J. Mater. Sci., 13, 1217-1223 (1978). 80Kaw: H. Kawamura, M. Matsumura, and S. Ushioda, J. Non-Cryst. Solids, 35-36, 1215-1220 (1980). 82Ips: H. Ipser, M. Gambino, and W. Schuster, Monatsh. Chem., 113, 389-398 ( 1982). 84Gla: V.M. Glazov, L.M. Pavlova, and D.S. Gaev, Izv. Akad. Nauk SSSR, Neorg. Mater., 20(9), 1476-1482 (1984) in Russian; TR: Russ. J. Inorg. Chem., 29(4), 620-624 (1984). Published in Bull. Alloy Phase Diagrams, 11(3), Jun 1990. Complete evaluation contains 3 figures, 4 tables, and 37 references. Special Points of the Ge-Se System