Фазовая диаграмма системы B-Pr

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B-Pr (Boron-Praseodymium) P.K. Liao and K.E. Spear Experimental work on the phase equilibria of the Pr-B system is sparse. The assessed phase diagram is from [76Spe]. The liquidus curves were largely estimated by correlating the melting behavior of the Pr-B system with the other RE boride systems. The REB66 phase found in many RE boride systems is not formed in the Pr-B system. The equilibrium phases are: (1) the liquid, L; ( 2) the terminal solid solutions, bcc (bPr) and dcph (aPr); (3) the terminal solid solution, rhombohedral (bB); and (4) three intermediate compounds, PrBx (x < 4), PrB4, and PrB6. (bB) and both (Pr) solid solutions have negligible composition ranges. The value for the melting temperature of PrBx (x < 4) has not been reported. If it melts as expected by a peritectic reaction, its melting temperature must be lower than the value for PrB4, because the latter phase melts peritectically to give the PrB6 plus a Pr-rich liquid. The melting temperature for PrBx (x < 4) has been estimated at 2000 с 300 C by [76Spe]. The homogeneity ranges of Pr borides are expected to be small, except perhaps for PrB6. [76Spe, 77Spe] discuss the rather wide homogeneity ranges 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] . 56Pos: B. Post, D. Moskowitz, and F.W. Glaser, J. Am. Chem. Soc., 78, 1800- 1802 (1956). 64Bli: G. Bliznakov and P. Peshev, J. Less-Common Met., 7, 441-446 (1964). 65Gie: R.F. Giese, Jr., J. Economy, and V.I. Matkovich, Z. Krist., 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) . 70Lee: K.N. Lee, R. Bachmann, T.H. Geballe, and J.P. Maita, Phys. Rev. B, 2(11) , 4580-4585 (1970). 71Hac: H. Hacker, Jr., Y. Shimada, and K.S. Chung, Phys. Status Solidi (a), 4, 459-465 (1971). 71Yaj: S. Yajima and K. Niihara, Preprint of paper presented at 9th Rare Earth Research Conference, Blacksburg, VA, 10-14 (1971). 72Fis: Z. Fisk, A.S. Cooper, P.H. Schmidt, and R.N. Castellano, Mater. Res. Bull., 7(4), 285-288 (1972). 76Spe: K.E. Spear, Phase Diagrams: Materials Science and Technology, Vol. 4, 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 17 references. Special Points of the Pr-B System