Фазовая диаграмма системы Ge-Pr

К оглавлению: Другие диаграммы (Others phase diargams)

Ge-Pr (Germanium-Praseodymium) A.B. Gokhale, A. Munitz, and G.J. Abbaschian The assessed Pr-Ge phase diagram is based primarily on [75Ere]. An error by [ 75Ere] in construction in the peritectic reaction of Pr3Ge (800 C) has been corrected. The melting temperatures of the pure components have been changed to conform with the currently accepted values. [75Ere] mentioned that Ge does not have an effect on the allotropic transformation temperature of Pr and indicated a transformation temperature of 774 C, which is significantly different from the currently accepted value of 795 C. This suggests that the thermal arrest observed by [75Ere] at 774 C may be due to a catatectic reaction involving (Pr). The reaction included in the assessed diagram indicates that the presence of Ge depresses the allotropic transformation temperature of Pr by 21 C. PrGe2 has been included because [58Mat], [64Gla], [67May], [68Sam1], [69Rud1], and [69Rud2] noted that it is isotypic with ThSi2. [67May] were able to synthesize PrGe2 at 550 C by the amalgam method. [69Rud2] and [67Lyn] indicated that PrGe2 is stable at the compositions 66.44 to 66.86 at.% Ge. Although [75Ere] did not prepare an alloy in this range, they indicated that PrGe2-x is isotypic with aGdSi2 at room temperature (the high-temperature form is ThSi2 type). These compositions (66.44 and 66.86 at.% Ge) are outside the composition limit given by [75Ere] for PrGe2-x. Because there are no indications that PrGe2 undergoes an allotropic transformation, the data of [ 75Ere] can be reconciled with the existence of PrGe2, if it is assumed that PrGe2 decomposes peritectically near the polymorphic transformation temperature of PrGe2-x. The thermal arrest observed by [75Ere] at 615 C may be due to both a polymorphic transformation of PrGe2-x and a peritectoidal decomposition of PrGe2, as shown in the assessed diagram. Because no other information is available on the homogeneity range for PrGe2-x using the data of [67Lyn] and [69Rud2], the range 66.44 to 66.86 at.% Ge is indicated in the assessed diagram. The solid solubility of Pr in (Ge) is less than 0.5 at.% at 700 C, and the solid solubility of Ge in (Pr) is less than 2 at.% at the eutectic temperature of 755 C [75Ere]. According to [68Sam2], [69Rud2], and [69Rud3], the character of the electrical resistivity of Pr5Ge3, PrGe, and PrGe2 changes from metallic to semiconducting type as a function of temperature at 526, 495, and 242 C, respectively. They explained the transition in terms of changes in the electron energy states of the intermediate phases. According to [58Mat], PrGe2 is ferromagnetic, with a transition temperature of 19 K. [66Bus] determined that PrGe becomes ferromagnetically ordered on cooling, with a magnetic transition temperature of 39 K. According to [67Bus], Pr5Ge3 has a N‚el temperature (TN) of 12 K and an asymptotic Curie temperature of 10 C. 58Mat: B.T. Matthias, E. Corenzwit, and W.H. Zachariasen, Phys. Rev., 112, 89 ( 1958). 64Gla: E.I. Gladyshevskii, Zh. Strukt. Khim., 5, 568-575 (1964) in Russian; TR: J. Struct. Chem., 5, 523-529 (1964). 66Bus: K.H.J. Buschow and J.F. Fast, Phys. Status Solidi, 16, 467-473 (1966). 66Hoh: D. Hohnke and E. Parthe, Acta Crystallogr., 20, 572-582 (1966). 67Bus: K.H.J. Buschow and J.F. Fast, Phys. Status Solidi, 21, 593-600 (1967). 67Lyn: K.A. Lynchak and T.Y. Kosolapova, Poroshk. Metall., (11), 92-96 (1967) in Russian; TR: Sov. Powder Metall. Met. Ceram., 6(11), 923-926 (1967). 67May: I. Mayer, E. Yanir, and I. Shidlovsky, Inorg. Chem., 6(4), 842-844 ( 1967). 68Sam1: G.V. Samsonov, Yu.B. Paderno, and B.M. Rud, Rev. Int. Hautes Temp. R‚fract., 5(2), 105-110 (1968). 68Sam2: G.V. Samsonov, Yu.B. Paderno, and B.M. Rud, Izv. V.U.Z. Fiz., (7), 105- 107 (1968) in Russian; TR: Sov. Phys. J., (7), 71-72 (1968). 69Rud1: B.M. Rud and K.A. Lynchak, Poroshk. Metall., (7), 51-54 (1969) in Russian; TR: Sov. Powder Metall. Met. Ceram., 8(7), 559-561 (1969). 69Rud2: B.M. Rud, K.A. Lynchak, and Yu.B. Paderno, Izv. Akad. Nauk SSSR, Neorg. Mater., 5, 1350-1353 (1969) in Russian; TR: Inorg. Mater., 5, 1152-1155 (1969) . 69Rud3: B.M. Rud, T.G. Kutsenok, and Yu.B. Paderno, Poroshk. Metall., (4), 34- 37 (1969) in Russian; TR: Sov. Powder Metall. Met. Ceram., 8(4), 284-287 (1969) . 75Ere: V.N. Eremenko, Q.C. Xuong, Yu.I. Buyanov, and A.M. Kharkova, Izv. Akad. Nauk SSSR, Neorg. Mater., 11, 160-162 (1975) in Russian; TR: Inorg. Mater., 11, 133-135 (1975). Published in Bull. Alloy Phase Diagrams, 10(3) Jun 1989. Complete evaluation contains 3 figures, 3 tables, and 25 references. Special Points of the Pr-Ge System