Phase diagram of the Y–Y{sub 2}Se{sub 3} system, enthalpies of phase transformations

• Published in: Journal of solid state chemistry 2015-10, Vol.230
• Main Authors: Andreev, O.V., Kharitontsev, V.B., Polkovnikov, A.A., Elyshev, A.V., Andreev, P.O.
• Format: Article
• Language: English
• Subjects: ANIONS; ELECTRIC CONDUCTIVITY; EUTECTICS; FUSION HEAT; HARDENING; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; LATTICE PARAMETERS; MELTING; MELTING POINTS; MICROHARDNESS; PHASE DIAGRAMS; PHASE TRANSFORMATIONS; SAMARIUM; SELENIUM; SOLID SOLUTIONS; TEMPERATURE DEPENDENCE; THERMAL ANALYSIS; VACANCIES; VALENCE; YTTRIUM SELENIDES
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/J.JSSC.2015.06.042

A phase diagram for the Y–Y{sub 2}Se{sub 3} system has been constructed in which the YSe and Y{sub 2}Se{sub 3} phases melt congruently. The daltonide type YSe phase (ST Y{sub 0,75}Se, a=1.1393 nm, melting point=2380 K, H=2200 MPa) forms a double-sided solid solution from 49–50–53 at% Se. In the 50–53 at% Se range, the unit cell parameter increases to 1.1500 nm, the microhardness increases to 4100 MPa and electrical resistivity increases from 0.018 to 0.114 Ω m. These changes are caused by the dominating influx of newly formed structural cationic vacancies arising from the selenium anions that are surplus for the 1:1 Y:Se stoichiometry. The full-valence Y{sub 2}Se{sub 3} composition exists as a low-temperature modification of ε-Y{sub 2}Se{sub 3} (ST Sc{sub 2}S{sub 3}, a=1.145 nm, b=0.818 nm, c=2.438 nm, melting point=1780 K, ∆fusion enthalpy=4±0.4 J/g) and transforms into a modification of ξ-Y{sub 2}Se{sub 3} that does not undergo fixing by thermo-hardening. The eutectic melting point between the YSe and Y{sub 2}Se{sub 3} phases is 1625±5 K, with a eutectic composition that is assumed to be 57.5 at% Se and have an enthalpy of fusion of 43±4.3 J/g. The eutectic for the Y and YSe phases appears at a temperature of 1600 K and 5 at% Se. - Highlights: • Phase equilibria in the Y–Y{sub 2}Se{sub 3} system from 1000 K to melt were studies. • High-temperature polymorphic transition for Y{sub 2}Se{sub 3} were observed. • Singular points in solid solutions areas for YSe and Y{sub 2}Se{sub 3} were found.