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An experimental approach employing temperature and concentration gradients is presented that is suitable for determining a sequence of solvus concentrations in a single experimental cycle. The Al-Mg-Si system is used as an example. Al solid solutions (''(Al)'') with different compositions and Mg 2 Si precipitates were equilibrated in the temperature range between 350 and 550 8C. The equilibrium compositions of (Al) were measured by energy dispersive X-ray spectroscopy in the transmission electron microscope. The coupled temperature-concentration values represent a path on the ternary solvus surface. Calphad calculations using different thermodynamic data sets were carried out to relate the experimental results to phase diagram evaluations. The measured solvus path agrees well with solvus data calculated with most recent thermodynamic parameter sets. The experimental approach can be applied to multicomponent alloys irrespective of their number of components with the same experimental effort. The efficiently generated solubility data are suitable to support phase diagram evaluations of multicomponent systems by the Calphad method.

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Seeding zone melting is applied to produce bulk Bi 1.625 In 0.375 Te 3 with 7.5 atom % In in solid solution. The concentration distribution is markedly homogeneous and exhibits pronounced anisotropic electrical and thermal conductivity. Subsequent precipitation from the solid solution leads to the formation of a highly anisotropic composite thermoelectric material consisting of aligned microscaled Bi 2 Te 3 and extended micro-to nanoscaled In 2 Te 3 plates. By the precipitation, an increase of zT by a factor of 6 compared with the parent supersaturated solid solution crystal is achieved. This is attributed to the combination of a decrease of In concentration from 7.5 to 3 atom % in the Bi 2 Te 3 layer and an increasing interface density due to the precipitation of In 2 Te 3 . The Bi 2 Te 3 /In 2 Te 3 interface is determined as coherent, and the crystallographic orientation between the two phases is determined as ⟨2̅ 11⟩ In2Te3 //⟨11̅ 00⟩ Bi2Te3 , {111} In2Te3 //{0001} Bi2Te3 .

Abstract

Experimental work using X-ray diffraction and differential scanning calorimetry was conducted on key samples in the Li–C binary system. Reproducible differential scanning calorimetry data with multiple heating cycles were produced only by samples sealed in arc welded Ta-capsules. Only one compound, α/βLi2C2, is found to be stable. A comprehensive Calphad-type assessment was performed and for the first time a consistent thermodynamic description, covering all thermodynamic and phase equilibrium data, is developed. Phase diagrams calculated from that validated database, including the gas phase, are presented. The phase LiC6, was also studied experimentally. It is metastable with respect to α/βLi2C2 + (C), but may be formed from Li + (C). Phase transitions of LiC6, claimed in the literature, are discussed.

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