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Evidence for a Phase Transition of β‐Gallium Oxide at Very Low Oxygen Pressures
Author(s) -
Fleischer Maximilian,
Höllbauer Leo,
Born Eberhard,
Meixner Hans
Publication year - 1997
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1997.tb03096.x
Subject(s) - oxygen , gallium , analytical chemistry (journal) , partial pressure , conductivity , oxide , bar (unit) , materials science , crystallite , electrical resistivity and conductivity , atmospheric temperature range , phase transition , chemistry , condensed matter physics , thermodynamics , metallurgy , physics , organic chemistry , chromatography , meteorology , electrical engineering , engineering
Depending on the operating temperature, gas sensors that are based on n‐type‐semiconductor, polycrystalline gallium oxide (Ga 2 O 3 ) thin films are used to detect oxygen (at temperatures, T, of 850°C) or reducing gases (T 900°C). At high temperatures (T 900°C), beta‐Ga 2 O 3 has an oxygen deficiency in the crystal lattice that is in dynamic equilibrium with the oxygen in the surrounding atmosphere. Variations in the conductivity of the sensor are caused by variations of the concentration of ionized oxygen vacancies. Therefore, a reduction in the proportion of oxygen or an increase in the concentration of reducing gases in the atmosphere in which the sensor is located leads to an increasing number of conducting electrons and, hence, an increasing conductivity. During a research project to investigate the long‐term stability of thin beta‐Ga 2 O 3 films in a variety of strongly reducing atmospheres at T > 600°C, a previously unknown phenomenon has been observed when measurements on low oxygen partial pressures (pO 2 10 ‐10 Pa (10 ‐15 bar)) have been made. A sharp decrease in sensor conductivity, by several orders of magnitude, is observed each time when pO 2 is reduced to a value of <10 ‐15 bar at temperatures in the range of ˜750°‐1000°C. The reason for this may be a phase transition in the β‐Ga 2 O 3 layer. However, attempts to freeze the new state with subsequent identification by X‐ray diffractometry have not succeeded in identifying the new phase.