Transition metal—Chalcogen systems, V.

Abstract

The iron—tellurium phase diagram was investigated by thermal, X-ray, and isopiestic measurements up to 1,100°C. Tetragonal β(≈FeTe_0.9) with a homogeneity range from 45.9 to 48.1 at % Te at 715°C is stable from room temperature to 844°C where it decomposes peritectoidally into Fe and rhombohedral high-temperature β′(≈FeTe_0.9). β′ decomposes at 914°C peritectically into Fe and liquid, and at 800°C by a eutectoid reaction into β and γ(≈FeTe_1.2). γ exists between 809° (γ→β′+δ) and 636°C (γ→β+δ). The monoclinically distorted NiAs-phase δ decomposes peritectically at 55.2 at % Te and 812°C into β′ and liquid and is stable down to the eutectoid δ⇋β+δ′ at 565±15°C and 58.8 at % Te. δ is separated from hexagonal NiAs-type δ′ by a narrow two-phase region. δ′ has a maximum range of homogeneity at 650°C from 59.2 to 65.1 at % Te and exists between the eutectoid δ′⇋β+ε at 519°C and the peritectic δ+L⇋δ′ at 766°C. Orthorhombic ε(≈FeTe_2.0) is stable from room temperature to the peritectic δ′+L=ε at 649°C. ε and Te form a degenerate eutectic at 446°C.