High Temperature Crystal Growth from the Vapour

Abstract

Experimental methods are presented which allow crystal growth and thermochemical studies up to 2500℃, in evacuated and electron-beam-sealed W-crucibles. Crystal growth from the vapour phase by chemical transport and sublimation; from the melt by solidification (Bridgman's). Phase diagram studies with DTA (Metter Thermoanalyser, SHT Furnace) up to 2400℃ in specially erroded W-capsules ( φ 4mm, length 10mm), sealed by electron beam. In this way no losses due to evaporation or changes of stoichiometry can take place. Vapour pressure measurements are made in the same apparatus or in a specially designed UHV-furnace capable of 2200℃ (Vacuum after baking 10^<-9> torr, when at temperature 10^<-6> torr). For equilibrium evaporation measurements, Knudsen cells made out of W are used (hole φ 0.1mm). For Langmuir free evaporation open cells and plates are used. Measurements of heats of formation or heats of reaction are made with our LKB Solution Calorimeter--Scanning Electron Microscopy with resolution of approximately 200A. Some examples of the use of these methods to investigate high temperature crystal growth phenomena are given concerning Surface roughning near the m.p. of solid-vapour interfaces Segregation of impurities at the interface during evaporation. Diffusion over the steps seems inhibited. Segregation of one component at the interface due to incongruent evaporation. Thermodynamics of high temperature evaporation in EuTe and YbTe between 900 and 2200℃. Phase diagram studies up to 2400℃.