Application of predominance diagrams in melt growth of oxides

Abstract

Equilibrium thermodynamic calculations are used to construct predominance diagrams of the Ti−O, Cr−O, and Zn−O systems and implications for the growth of Ti:Sapphire, ruby, and ZnO crystals are discussed. For each of these systems, a growth atmosphere yielding an oxygen partial pressure that stabilizes the desired oxidation state of the metal is proposed on the basis of the performed computations. The effectiveness of these atmospheres is demonstrated in crystal growth experiments.

Thermodynamic Analysis of ZnO Crystal Growth from the Melt

“…Because the oxide construction parts are often stable at rather low temperatures and oxide crystal almost decompose at high temperatures, both conditions are accomplished if (PO 2 ) min < (PO 2 ) eq < (PO 2 ) max . Commonly, amounts of oxygen, 1 -2 vol% [27] in the case of GGG growth, are added into the growth atmosphere to prevent volatile oxides. However, this value (PO 2 ) often is more than (PO 2 ) max at lower temperatures.…”

“…Temperature dependence of PO 2 with comparing different gases in this reaction is shown in Figure 5. Using CO 2 at a total pressure of approximately 10 bars, Ganschow et al [27] have successfully grown ZnO crys tals from the melt in a Bridgman-like configuration.…”

On Thermodynamic Aspects of Oxide Crystal Growth

“…This is the case, for example, for wüstite FeO and olivine (Fe,Mg) 2 SiO 4 [10]-both containing Fe 2+ . These phases are stable only in a corridor p min O 2 (T) < p O 2 < p max O 2 (T), and the lower and upper limits rise with temperature T. It was demonstrated, however, that also under such conditions, "dynamic atmospheres" containing mixtures of CO 2 and CO often can deliver some p O 2 (T), which stabilizes the desired oxidation state over a wide T range [11,12]. Thermogravimetric measurements with aegirine (NaFe 3+ Si 2 O 6 ) nanocatalysts showed mass losses up to 25% during heating to 700 °C in air.…”

Growth Measures to Achieve Bulk Single Crystals of Transparent Semiconducting and Conducting Oxides

“…Iridium easily oxidizes at low and moderate temperatures (roughly 600-1200 C), but it is substantially intact at high temperatures. More details on using such dynamic, self-adjusting growth atmospheres can be found in Refs [72][73][74]. CO 2 decomposes into CO þ 1 / 2 O 2 , thus providing more oxygen with increasing temperatures.…”