Lithium, zinc oxide doped with

Now we will overview some experiments that reveal the specificities of the Jahn-Teller effect in diluted crystals. First of all, we will discuss a justification of their relaxation origin. We have mentioned before that the first experiments were done on the crystals of aluminum oxide (corundum), yttrium aluminum garnet, yttrium iron garnet, and lithium gallium spinel doped with a number of 3d ions [10,11]. The main result was the discovery of attenuation maximum which was considered to be observed at cot 1 and reconstruction of the relaxation time temperature dependence. In some experiments reported later both the velocity and attenuation of ultrasound were measured as functions of the temperature. They were done on ZnSe and ZnTe crystals doped with transition metals. These crystals have the zinc-blende structure with the Jahn-Teller ion in tetrahedral coordination. The following... 

Spectral dependence of the photoadsorption of oxygen on powdered samples of pure zinc oxide or sine oxide doped with lithium or aluminium has been studied by Zakharenko et al. [127] whose results provided... 

Because of the potential importance for industrial-scale catalysis, we decided to check (i) whether an influence of a semiconductor support on a metal catalyst was present also if the metal is not spread as a thin layer on the semiconductor surface but rather exists in form of small particles mixed intimately with a powder of the semiconductor, and (ii) whether a doping effect was present even then. To this end the nitrates of nickel, zinc (zinc oxide is a well-characterized n-type semiconductor) and of the doping element gallium (for increased n-type doping) or lithium (for decreased n-type character) were dissolved in water, mixed, heated to dryness, and decomposed at 250°-300°C. The oxide mixtures were then pelleted and sintered 4 hr at 800° in order to establish the disorder equilibrium of the doped zinc oxide. The ratio Ni/ZnO was 1 8 and the eventual doping amounted to 0.2 at % (75). 

The nonstoichiometry of an oxide strongly depends on the presence of alio-valent impurities and dopants affect the number of thermal defects in non-stoichiometric oxides and their electrical conductivity because the solutes have a valence other than the atoms they replace. This is illustrated in the case of lithium and chromium doping of nickel and zinc oxides in equilibrium with gaseous oxygen. 

In order to quantitatively appreciate the effect of doping, let us examine the first case of lithium ions introduced in substitution of Zn ions in zinc oxide, at equilibrium with the oxygen. Zinc oxide exhibits overstoichiometry of zinc, which results in the presence of zinc ions in an interstitial position and free electrons. The equilibrium with oxygen is written as follows ... 

Zinc oxide crystals can exhibit strong piezoelectric properties. Normally recognized as an n-type semiconductor, it has a resistivity less than 103 ohm-cm. When doped with lithium, resistivity rises to 1012 ohm-cm and it exhibits piezoelectricity about four times that of quartz. 

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