Фазовая диаграмма системы B-Ho

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B-Ho (Boron-Holmium) P.K. Liao and K.E. Spear Little experimental work has been performed on the phase equilibria for the Ho- B system. The assessed phase diagram is from [76Spe]; it is largely estimated and is expected to be very similar to that for the Dy-B system. The presence of a 1-atm vapor phase is included in the assessed diagram. In addition to the vapor, the equilibrium phases are (1) the liquid, L; (2) the terminal solid solutions, cph (aHo) and bcc (bHo); (3) the terminal solid solution, rhombohedral (bB); and (4) five intermediate compounds, HoB2, HoB4, HoB6, HoB12, and HoB66. (bB) and (Ho) solid solutions have negligible composition ranges. The melting behavior and melting temperatures of the Ho-boride phases are not known in most cases. However, they are expected to be similar to the Dy-B system. The only experimental data for melting temperatures in the Ho-B system is that for HoB6 by [68Mor]; they reported that the HoB6 phase melts at 2180 C, but the type of melting reaction was not given. The homogeneity ranges of the Ho borides are expected to be small, except for HoB6, but no experimental results were found. [76Spe] discussed the rather wide homogeneity ranges and resulting defect structures for a number of REB6 phases. All available experimental data indicate that the hexaboride is stoichiometric at its metal-rich phase boundary and becomes B-rich by the formation of up to approximately 30% metal vacancies [76Spe, 77Spe]. 59Eic: H.A. Eick and P.W. Gilles, J. Am. Chem. Soc., 81, 5030-5032 (1959). 61Lap: S. LaPlaca, I. Binder, and B. Post, J. Inorg. Nucl. Chem., 18, 113-117 ( 1961). 62Lap: S.J. LaPlaca, Brookhaven National Laboratory, private communication ( 1962); quoted in [64Pos]. 64Pos: B. Post, Boron, Metallo-Boron Compounds, and Boranes, R.M. Adams, Ed., Interscience, New York, 301-371 (1964). 65Gie: R.F. Giese, Jr., J. Economy, and V.I. Matkovich, Z. Kristallogr., 122, 144-147 (1965). 68Mor: O.A. Mordovin and E.N. Timofeeva, Russ. J. Inorg. Chem., 13(12), 1627- 1629 (1968). 70Car: J.-O. Carlsson and T. Lundstrom, J. Less-Common Met., 22, 317-320 (1970) . 71Pad: Yu.B. Paderno, V.V. Odintsov, I.I. Timofeeva, and L.A. Klochkov, High Temp., 9(1), 175-177 (1971). 72Fis: Z. Fisk, A.S. Cooper, P.H. Schmidt, and R.N. Castellano, Mater. Res. Bull., 7(4), 285-288 (1972). 72Sch: K. Schwetz, P. Ettmayer, R. Kieffer, and A. Lipp, J. Less-Common Met., 26, 99-104 (1972) in German. 73Bau: J. Bauer and J. Debuigne, C.R. Acad. Sci. Paris, Ser. C, 277, 851-853 ( 1973). 76Spe: K.E. Spear, Phase Diagrams, Vol. 4, Materials Science and Technology, Academic Press, New York, 91-159 (1976). 77Cal: B. Callmer, Acta Crystallogr. B, 33, 1951-1954 (1977). 77Spe: K.E. Spear, Boron and Refractory Borides, V.I. Matkovich, Ed., Springer- Verlag, New York, 439-456 (1977). Submitted to the APD Program. Complete evaluation contains 1 figure, 3 tables, and 23 references. Special Points of the Ho-B System