Preparation of yttrium silicides and oxide-silicides

Add time:07/29/2019    Source:sciencedirect.com

Structures and phase compositions in the YSi system are reviewed. Thermal analyses, metallography, X-ray diffraction and hardness measurements have been used to examine the system. Y5Si3 is confirmed as the most stable congruently melting silicide, metal vacancies may be present in the structure of Y5Si3+x materials when it is made as part of a two-phase system with Y5Si4. It has proved impossible to prepare Y5Si4 as a pure phase. YSi is confirmed as a peritectic phase with an 1836 °C peritectic line terminating at 51.3 at.% Si. Two eutectic points have been confirmed and established. It is concluded that Y3Si5 is the highest siliconcontaining silicide arising from high temperature arc preparation. Tin has been used as an auxiliary metal bath in low temperature preparations which yield fine crystals of a higher silicide than Y3Si5 approaching more closely to YSi2 for all the Y:Si ratios used in the solvent. An orthorhombic unstable phase with composition close to Y3Si2, but probably containing some tin, is the only other silicide prepared from the auxiliary bath. High temperature preparations of Y5Si3Ox, Y3Si2Ox and Y2Si3Ox compositions show the effect oxygen can have on the silicide preparations. Y5Si3 dissolves oxygen to Y5Si3O0.6 and the effect is a steadily decreasing lattice parameter. Higher oxygen contents lead to decomposition and an oxygenstabilized Y3Si2 phase which has a Y5Si4-type structure. YSi dissolves little oxygen and appears unaffected whilst oxygen in Y3Si5 leads to lower Si/Y stoichiometry, around Y2Si3, for the highest silicon content phase.

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