Investigation of Ga Substitution in ZnO Powder and Opto-Electronic Properties

Abstract

Two sets of Ga-doped ZnO powders were synthesized via solid-state and Pechini routes with a substitution rate varying from 0 to 4 mol %. The gallium solubility limit is strongly dependent on the synthesis history. Indeed, a low temperature annealing allows incorporating about 1.5 mol % (X-ray diffraction (XRD), inductive coupled plasma spectroscopy (ICP), optical properties) whereas under 0.1% of dopant is introduced after thermal treatment at high temperature: 1500 degrees C (from XRD and pellets conductivity). The incorporation of gallium leads to an anisotropic distortion of the zincite crystal lattice (a and c parameters increase and decrease, respectively, versus the Ga content leading to a decrease of the c/a ratio) which can be explained from the valence bond model. XRD analysis, chemical titration by ICP, and conductivity measurements (on pellets obtained at high temperature) allow determining accurately the maximum Ga content in the zincite. The optical properties (IR absorption efficiency) linked to electron carriers are directly correlated to the gallium rate introduced in ZnO oxide; nevertheless, the non linear correlation between these two parameters tends to show that the concentration of charge carriers in the system is not equal to the amount of Ga(3+) atoms inserted per ZnO volume unit. A saturation regime is observed and was here explained once again on the basis of the valence band model by the increase of inhibiting p type defects with the increase of (n-type donors) Ga(3+) concentration.

A review of thermoelectric ZnO nanostructured ceramics for energy recovery

“…Among the thermoelectric materials, zinc oxide displays a good seebeck coefficient value, a high thermal stable temperature ranges and low environmental impact [22,23]. The different investigations on ZnO materials present that their thermoelectric properties can be improved by substitution with different element such as Aluminum [1][2][3][4][24][25][26][27][28], Cerium and Dysprosium [29], Gallium [6,[30][31][32], Indium [33], praseodymium [34], Antimony [20] and Nickel [7,19]. Therefore, ZnO as thermoelectric materials is slowly developing, but surely gaining attention as one of the candidates for thermoelectric applications.…”

Visible-transparent and UV/IR-opaque colloidal dispersions of Ga-doped zinc oxide nanoparticles

“…2 In a typical procedure, zinc acetate dihydrate (Sigma, purity ≥99%) was first dissolved in DEG (99% Sigma). The gallium source (Solvay, acid solution of gallium nitrate, Ga: 128 g/L, [H + ] = 0.29 M) was added to the raw mixture in a round flask equipped with a condenser.…”

“…2a) was compatible for the aliovalent doping with Ga 3+ cation. 2 The size of the crystallites Nevertheless, these particles are too large and scatter visible light even when they are dispersed in liquid media. Therefore the dispersion was not transparent preventing these particles to fulfil the requirements for glazing application.…”

“…1 Our own recent results demonstrated that aluminum or gallium-doped ZnO are promising candidates for getting efficient infrared absorbing powders. 2 Two kinds of devices may be engineered: dense and thin films, 3 or more original systems such as varnishes and coatings added or spread to the glazing in which TCO nanoparticles are dispersed in a glass or polymeric matrix. 4 At the present time, these films are produced by physical processes, e.g.…”

Synthesis of heavily doped nanocrystalline ZnO:Al powders using a simple soft chemical method

“…Doping of ZnO with metal ions is an easy way to tailor its electronic and optical performance and improve its application potential. For example, if the added dopant is Al, its conductivity increases without impairing the optical transmission [17,18]. Since a supplementary free electron is created upon the non-aliovalent substitution of Al 3?…”