Hydrothermal growth and structural studies of Si1-xGexO2 single crystals

The substitution of germanium in the α-quartz structure is a method investigated to improve the piezoelectric properties and the thermal stability of α-quartz. Growth of α-quartz type Si(1-x)Ge(x)O(2) single crystals was performed using a temperature gradient hydrothermal method under different experimental conditions (pressure, temperature, nature of the solvent, and the nutrient). To avoid the difference of dissolution kinetics between pure SiO(2) and pure GeO(2), single phases Si(1-x)Ge(x)O(2) solid solutions were prepared and used as nutrients. The influence of the nature (cristobalite-type, glass) and the composition of this nutrient were also studied. Single crystals were grown in aqueous NaOH (0.2-1 M) solutions and in pure water. A wide range of pressures (95-280 MPa) and temperatures (315-505 °C) was investigated. Structures of single crystals with x = 0.07, 0.1, and 0.13 were refined, and it was shown that the structural distortion (i.e., θ and δ) increases with the atomic fraction of Ge in an almost linear way. Thus, the piezoelectric properties of Si(1-x)Ge(x)O(2) solid solution should increase with x, and this material could be a good candidate for technological applications requiring a high piezoelectric coupling factor or high thermal stability

The changes in lead silicate glasses induced by the addition of a reducing agent (TiN or SiC)

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The characterization of waste cathode-ray tube glass

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Hydrothermal growth of large piezoelectric single crystals of GaAsO4

International audienceGaAsO4 crystals were grown by a hydrothermal epitaxial process. Micro crystalline GaAsO4 powder was first synthesized by hydrothermal methods by using GaAs as a starting material in a sulfuric acid solvent under oxidizing conditions. Experimental conditions were optimized and the yield of the nutrient synthesis reached 88%. GaAsO4 powder was then used as the nutrient for growing GaAsO4 single crystals by epitaxy on (2(1) over bar 0) oriented GaPO4, AlPO4 and GaAsO4 plates. Crystal growth was performed in a horizontal PTFE-lined autoclave divided into two parts using sulfuric acid as the solvent under a slow heating gradient. Hydrothermal conditions were optimized in order to improve the crystal quality. The influence of the nature and orientation of the seeds on the growth rate was studied. From the solubility curve, the solute supply Delta S as a function of temperature during the growth process was calculated. Transparent crystals were obtained with Delta S between 0.002 and 0.009 mol/L. Large crystals (3.9 Chi 1.8 Chi 1.4 cm(3)) of gallium arsenate were obtained. These crystals were cut into (2(1) over bar 0), (010) and (001) plates. Mapping using Raman spectroscopy was performed in order to study the growth recovery on the seed. GaAsO4 crystals were characterized by infrared spectroscopy in order to quantify the amount of OH groups in the crystal structure. A low value of the absorption coefficient a at 3300 cm(-1) was measured 0.067 cm(-1) indicating a good crystal quality. Optical measurements were performed on GaAsO4 crystals by UV-vis-NIR spectrophotometry. Gallium arsenate exhibits the highest value of birefringence in the alpha-quartz group with Delta n =0.033. The transmission in the spectral region above 250 nm yields a bandgap of 5.85 eV. Piezoelectric properties were measured on resonators. An electromechanical coupling coefficient of 20% was measured which is the highest in the alpha-quartz group. A quality factor QF of 3.2 Chi 10(10) was obtained on a Y-cut plate. The C-66 elastic constant was found to be 20 GPa

In situ X-ray Absorption Spectroscopy Study of Si(1-x)GexO2 Dissolution and Germanium Speciation under Hydrothermal Conditions

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Elaboration and characterization of foam glass from cathode-ray tubes

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Characterisation of porous glasses prepared from cathode ray tube (CRT)

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