Фазовая диаграмма системы Cr-Se

К оглавлению: Другие диаграммы (Others phase diargams)

Cr-Se (Chromium-Selenium) M. Venkatraman and J.P. Neumann The assessed Cr-Se phase diagram below ~1000 C is adopted from [87Bla]. The high-temperature region involving the solid-liquid phase equilibria is speculative; except for the melting point of CrSe(HT) [61Cor] and two points on the Se-rich liquidus curve quoted by [75Bab], no data are available in this region. Similar to the Cr-S system, the existence of a liquid miscibility gap between the metal-rich liquid L1 and the Se-rich liquid L2 is assumed. The liquidus points by [75Bab] indicate that, similar to the Cr-Te system, no liquid miscibility gap exists in the Se-rich region. The liquidus point at 1500 C and 60 at.% Se is an estimate by [73Bar]. The Cr-Se phase diagram is characterized by the occurrence of several intermediate phases in the solid state between approximately 50 to 60 at.% Se. Similar to the Cr-S system, the existence of the following intermediate phases has been clearly established: CrSe(HT) (hexagonal), CrSe(LT) (hexagonal), Cr7Se8 (monoclinic), Cr3Se4 (monoclinic), Cr2Se3(I) (hexagonal), and Cr2Se3(II) (rhombohedral). In addition to these equilibrium phases, the following selenides have been reported-Cr1.03Se [75Bab], Cr2Se3(III) [87Bla], Cr5Se8 [ 69Sle], and CrSe2 [80Bru]. These phases are either questionable or metastable at ambient temperature and pressure. The assessed phase diagram shows the equilibrium with Se(liquid), L2, at P >1 bar. No measurements of the boundaries of the two-phase region CrSe(LT) + L2 have been carried out, but the Se-rich phase boundary of the CrSe(LT) phase in equilibrium with Se(liquid) must lie at a higher Se content than the one corresponding to the equilibrium with Se(gas) at 1 bar. The temperature of the catatectic reaction CrSe(LT) = Cr2Se3(II) + L2 is taken from [80Zhe]. The temperature of the eutectic reaction L2 = Cr2Se(II) + (gSe) is taken from [ 87Bla]; it is ~1 C below the melting temperature of pure gSe [Melt]. All intermediate selenide phases are essentially modifications of the prototype NiAs (B81) structure, which is represented by the CrSe(HT) phase. Analogous to the Cr-S system, the structures of the selenide phases are characterized by the presence of vacancy defects on Cr-sites; the distribution of the vacancies ranges from random to highly ordered. The vacancy concentration increases with increasing Se content, tending toward the CdI2 ( C6) structure. CrSe(HT) has the true NiAs-type structure with a random distribution of vacancies over all Cr layers. In CrSe(LT), the vacancies occur only in alternate Cr layers; within these layers, the distribution of the vacancies is random. The transition temperature between these phases is approximately 1100 C [87Bla]. Based on the presence of a distinct anomaly in the electrical conductivity [ 67Iva] and the observation of thermal effects at 305 C [75Bab], the existence of Cr1.03Se was suggested by [75Bab]. An analogous phase is known to exist in the Cr-S system. However, [87Bla] could not detect this phase, despite long annealing times. [87Bla] suggested that the anomaly at 305 C is not due to a polymorphic transformation, but that it is related to the eutectoid decomposition of CrSe(LT) into (Cr) and Cr7Se8 at 362 C. Because the existence of Cr1.03Se is questionable, it is not shown in the assessed diagram. The solubility of Se in (Cr) was not determined, but it is suggested that it is very small, similar to that of S in (Cr). Based on their measurements of the partial pressure of Se corresponding to the equilibrium between Cr2Se3(II) and Se (liquid), [80Zhe] concluded that the solubility of Cr in liquid Se is small. Cr2Se3(III) was prepared by [87Bla] in the presence of elemental Se by quenching from elevated temperatures (800 to 1100 C). Apparently, it forms from the hexagonal high-temperature CrSe(LT) phase, which, on quenching, undergoes a monoclinic distortion. On heating, the phase decomposes to Cr2Se3( II) and (Se) [87Bla]. CrSe2 was prepared by oxidation of KCrSe2 with I2 in acetonitrile at ambient temperature [80Bru]. It has the hexagonal CdI2-type crystal structure. On heating, it decomposes at ~300 C irreversibly to Cr2Se3( II) and Se [80Bru]. [68Bat] prepared CrSe by shock loading a mixture of Cr and Se powders. [69Sle] prepared the intermediate phase Cr5Se8 at 1200 C under a pressure of 65 kbar. It is not known if the phase is stable at ambient pressure. Similar to the Cr-S system, the magnetic behavior of the selenides is very complex; it depends strongly on their defect structure. Most of the intermediate phases are semiconductors; at higher temperatures, all phases are paramagnetic, becoming antiferromagnetic below room temperature. Only alloys in the homogeneity range of the Cr3Se4 phase near ~58 at.% Se appear to become ferro- or ferrimagnetic at very low temperatures [38Har, 73Yuz, 80Mau]. CrSe(HT) or (LT) exhibits metallic conductivity. Near 50 at.% Se, CrSe(LT) can be retained easily at room temperature by even moderately slow cooling from higher temperatures [87Bla]. CrSe(LT) becomes antiferromagnetic below room temperature. At 50 at.% Se, the following N‚el temperatures were reported: 279 K [60Tsu], 235 K [57Lot], 285 K [62Mas], 276 с 4 K [78Mak] and 275 с 3 K [ 80Mak]. The N‚el temperature decreases with increasing Se concentration [60Tsu] to 279 K (50.0 at.% Se), 271 K (51.0 at.% Se), and 232 K (51.7 at.% Se). Cr7Se8 appears to be a semiconductor [62Mas]. It is paramagnetic above 100 K; the magnetic susceptibility exhibits an anomaly at 92 K [62Mas]. In contrast to [62Mas], metallic conductivity was observed by [64Che]. The explanation for these contradictory results might be the slow reaction kinetics of the formation of Cr7Se8 from CrSe(LT); even after a year, the eutectoid reaction was not completed [87Bla]. Cr3Se4 is a semiconductor. According to [79Bab], the N‚el temperature of stoichiometry Cr3Se4 (57.1 at.% Se) has a value of 173 K, not ~80 K, as reported in other investigations. The magnetic and electrical properties of stoichiometric Cr3Se4 show clearly the presence of a transition at ~80 K [ 81Pei], but it does not correspond to the antiferromagnetic N‚el temperature [ 81Pei]. Cr-rich Cr3Se4 in the composition range 55.2 to 57.1 at.% Se is antiferromagnetic at low temperatures; the temperature of the magnetic transition increases from 15 K (55.2 at.% Se) to 88 K (57.1 at.% Se) [80Mau]. Se-rich Cr3Se4 in the composition range 57.1 to 58.8 at.% Se exhibits ferromagnetic [80Mau] or ferrimagnetic [73Yuz] behavior at low temperatures. The magnetic and electrical behavior of Cr2Se3(I) in the composition range 59 to 60 at.% Se is very complicated and requires clarification. The behavior is very sensitive to variations in heat treatment and composition. Some of the discrepancies among earlier studies might be explained by the only recently reported observation that Cr2Se3(I) is not stable below ~500 C [87Bla]. It appears that Cr2Se3(I) is a semiconductor [85Pei]. Cr2Se3(II) is a metallic conductor [76Bab]; it becomes antiferromagnetic below the N‚el temperature of 43 K [73Yuz] or 42 K [80Bru]. Cr5Se8 exhibits metallic conductivity; it is paramagnetic at room temperature, antiferromagnetic between 250 and 100 K, and ferromagnetic below 100 K [69Sle]. 27Jon: W.F. de Jong and H.W.V. Willems, Physica, 7, 74-79 (1927) in Dutch. 38Har: H. Haraldsen and F. Mehmed, Z. Anorg. Allg. Chem., 239, 369-394 (1938) in German. 56Tsu: I. Tsubokawa, J. Phys. Soc. Jpn., 11(6), 662-665 (1956). 57Lot: F.K. Lotgering and E.W. Gorter, J. Phys. Chem. Solids, 3, 238-249 (1957) . 60Tsu: I. Tsubokawa, J. Phys. Soc. Jpn., 15(12), 2243-2247 (1960). 61Che: M. Chevreton and F. Bertaut, Compt. Rend. Paris, 253(1), 145-147 (1961) in French. 61Cor: L.M. Corliss, N. Elliott, J.M. Hastings, and R.L. Sass, Phys. Rev., 122( 5), 1402-1406 (1961). 62Ber: E.F. Bertaut, A. Delapalme, F. Forrat, G. Roult, F. de Bergevin, and R. Pauthenet, J. Appl. Phys., 33(3), 1123-1124 (1962). 62Mas: K. Masumoto, T. Hihara, and T. Kamigaichi, J. Phys. Soc. Jpn., 17, 1209- 1210 (1962). 64Che: M. Chevreton, Ph.D. thesis, University of Lyon, France (1964) in French. 67Dor: L.M. Doronina, V.S. Filatkina, and S.S. Batsanov, Izv. Akad. Nauk SSSR, Neorg. Mater., 3(9), 1696-1697 (1967) in Russian; TR: Inorg. Mater., 3(9), 1482-1484 (1967). 67Iva: V.A. Ivanova and G.M. Aliev, Izv. Akad. Nauk SSSR, Neorg. Mater., 3(8), 1490-1491 (1967) in Russian; TR: Inorg. Mater., 3(8), 1299-1301 (1967). 68Bat: S.S. Batsanov and E.S. Zolotova, Dokl. Akad. Nauk, SSSR, 180(1), 93-94 ( 1968) in Russian; TR: Dokl. Chem., 180, 383-384 (1968). 68Che: M. Chevreton and B. Dumont, Compt. Rend. Paris, Ser. C, 267, 884-887 ( 1968) in French. 69Sle: A.W. Sleight and T.A. Bitter, Inorg. Chem., 8, 566-569 (1969). 70Weh: F.H. Wehmeier, E.T. Keve, and S.C. Abrahams, Inorg. Chem., 9(9), 2125- 2131 (1970). 71Kje: A. Kjekshus and W.E. Jamison, Acta Chem. Scand., 25, 1715-1721 (1971). 73Bab: D. Babot and M. Chevreton, J. Solid State Chem., 8, 166-174 (1973) in French. 73Bar: K.G. Barraclough and A. Meyer, J. Cryst. Growth, 20, 212-216 (1973). 73Yuz: M. Yuzuri, J. Phys. Soc. Jpn., 35, 1252 (1973). 75Bab: A.A. Babitsyna, M.A. Chernitsyna, and V.T. Kalinnikov, Zh. Neorg. Khim., 20, 3357-3362 (1975) in Russian; TR: Russ. J. Inorg. Chem., 20(12), 1855-1858 (1975). 76Bab: D. Babot, G. Peix, and M. Chevreton, J. Phys. Orsay Fr., 37(10), C4/111- C4/115 (1976) in French. 78Mak: G.I. Makovetskii and G.M. Shakhlevich, Phys. Status Solidi (a), 47, 219- 222 (1978). 79Bab: D. Babot, M. Chevreton, J.L. Buevoz, R. Lagnier, B. Lambert-Andron, and M. Wintenberger, Solid State Commun., 30, 253-257 (1979) in French. 80Bru: C.F. van Bruggen, R.J. Haange, G.A. Wiegers, and D.K.G. de Boer, Physica B, Amsterdam, 99, 166-172 (1980). 80Mak; G.I. Makovetskii and G.M. Shakhlevich, Phys. Status Solidi (a), 61, 315- 322 (1980). 80Mau: A. Maurer and G. Collin, J. Solid State Chem., 34, 23-30 (1980). 80Zhe: V.A. Zhegalina, Z.S. Arakelyan, V.T. Kalinnkov, and Ya.Kh. Gringerg, Zh. Neorg. Khim., 25(10), 2807-2813 (1980) in Russian; TR: Russ. J. Inorg. Chem., 25(10), 1547-1551 (1980). 81Pei: G. Peix, D. Babot, and M. Chevreton, J. Solid State Chem., 36, 161-170 ( 1981) in French. 83Oht: T. Ohtani, R. Fujimoto, H. Yoshinaga, M. Nakahira, and Y. Ueda, J. Solid State Chem., 48, 161-167 (1983). 85Pei: G. Peix, D. Babot, and M. Chevreton, J. Solid State Chem., 56, 304-317 ( 1985) in French. 87Bla: R. Blachnik, G.P. Gunia, M. Fischer, and H.D. Lutz, J. Less-Common Met., 134, 169-177 (1987) in German. Submitted to the APD Program. Complete evaluation contains 2 figures, 3 tables, and 50 references. Special Points of the Cr-Se System