O. Cambon

Structural disorder and loss of piezoelectric properties in α-quartz at high temperature

The piezoelectric properties of α-quartz-based resonators, characterized by the mechanical quality factor, Q, are found to degrade beginning above 300u200a°C. This is well below the transition at 573u200a°C to the β phase, which in principle limits the piezoelectric response of this material. This gradual loss of piezoelectric response can be linked to the increase in structural disorder in α-quartz found in total neutron scattering measurements. Analysis of these data by reverse Monte Carlo modeling indicates that between 200 and 400u200a°C, the local disorder in the instantaneous structure of α-quartz becomes comparable to that of β-quartz.

Growth and dielectric characterization of large single crystals of GaAsO4, a novel piezoelectric material

AbstractGallium arsenate (GaAsO 4 )isanew α -quartz-type piezoelectric material. Large single crystals (8 mm along the c -direction) were grownfor thefirst timeby hydrothermal methods. The different crystal faces wereindexed by X-ray diffraction. The crystal quality was characterizedby infrared measurements. X -and Z -cut crystals were prepared in order to perform dielectric measurements. The dielectric constants ofGaAsO 4 ( e 11 =8 . 5, e 33 = 8 . 6) are the highest found among α -quartz type materials. A linear relationship has been established between astructural property, the tetrahedral tilt angle δ , and the dielectric constants for the well-known α -quartz homeotypes. These results indicatethat gallium arsenate should have the highest piezoelectric coupling coefficient of any material of this family. uf6d9 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved. 1. IntroductionQuartz material is currently the most used piezoelectricmaterial. Nevertheless, its properties are limited for certainapplications due to its low electromechanical couplingcoefficient. GaAsO

Advances in crystal growth and characterizations of gallium orthophosphate, GaPO4

Abstract Gallium orthophosphate, GaPO 4 , is a piezoelectric material isostructural with α -quartz, SiO 2 , with better piezoelectric characteristics: higher coupling coefficient for its temperature compensated cut and wider thermal stability (up to 933°C). A new investigation of the solubility of GaPO 4 in different acids and their mixtures allows to determine the metastable zone of which the knowledge is primordial for a good growth restart. The comparison of experimental growth results obtained in horizontal glass vessels ( T c T c >170°C) leads to specify a necessary minimum value of the solute supply at the interface crystal/solution. On the other hand, natural large seeds being not available, the seed lengthening is carried out with the splicing technique followed by crossed crystal growths to decrease the density of structural defects. At the same time, characterizations of crystals have been undertaken to check: the OH content by infrared spectroscopy; the crystalline quality (specially crystals after splicing) and the growth restart by X-ray topography; the piezoelectric properties.

Piezoelectric characterization and thermal stability of a high-performance α-quartz-type material, gallium arsenate

Piezoelectric measurements were performed on large single crystals (8 mm along the c direction) of an α-quartz-type piezoelectric material, gallium arsenate, GaAsO4, which allow us to extend the structure-property relationships in the α-quartz-type materials. These first measurements on Y-rotated-cut plates have shown that gallium arsenate is the highest-performance piezoelectric material of this group. As compared to the coupling coefficients of the other materials with the same structure (kSiO2=8%, kAlPO4=11%, and kGaPO4=16%), gallium arsenate exhibits the highest piezoelectric coupling coefficient of about 22%, as has been predicted by the structure-property relationships. Moreover, from these piezoelectric measurements, the C66′ elastic constant was determined and compared with elastic constants in quartz-type materials. The proposed value for the cut angle of the AT plane in GaAsO4 is −6.3°. In order to extend the previous thermal stability results, thermal gravimetric analysis (TGA) and x-ray diffra...

Crystal growth of GaPO4, a very promising material for manufacturing baw devices

GaPO4 cystals were obtained by hydrothermal solution crystal growth. The retrograd solubility of the material was investigated in different solvents. In static growth vessels, good quality crystals can be obtained only if the solute supply is higher than about 0.06M/L. Crystal characterization by infrared spectroscopy showed that dilute solvents at high temperature decrease the “-OH” group content. Seed lengthening by splicing along the Y-axis was designed. The AT cut angle and the C44 elastic constant were determined. Compared to quartz-type materials, the C0/C1 calculation shows the high ability of GaPO4 for manufacturing BAW devices.

Ultra stable oscillators dedicated for space applications: oscillator and quartz material behaviors vs radiation

This paper presents the first results obtained in the R&D study initiated by the CNES at the end of 2004. Numerous French experts have been gathered to determine and to tentatively understand the mechanisms responsible for the radiation sensitivity of quartz resonators and to correlate the results of various analyses in order to reduce or to anneal their susceptibilities

Characterization of unswept and swept quartz crystals for space applications

Unswept and vacuum-swept synthetic quartz crystals were investigated in order to determine the mechanisms responsible for the radiation sensitivity of this material. Results were obtained by means of infrared (IR) spectroscopy, dielectric relaxation spectroscopy (DRS), and thermoluminescence (TL). First, the effect of vacuum sweeping was clearly demonstrated in IR absorption by a significant decrease in the amount of hydroxyl ions and in DRS by the disappearance of the dielectric loss peak arising from the relaxation of alkali ions. Second, it was shown that swept quartz is less sensitive to irradiation than the unswept crystal. A sharp decrease in the TL sensitivity of the electrolyzed material was observed in the energy range corresponding to the recombination of alkaline-electronic defects. DRS results indicated that the dielectric signal is shifted toward a lower energy range for both types of crystals, suggesting that the irradiation greatly facilitates the relaxation of alkaline species by creating ...

Solubilite´et croissance de la berlinite AlPO4, en milieu phospho-sulfurique

Abstract La solubilite´de la berlinite, AlPO 4 , ae´te´mesure´e dans des me´langes dacide phosphorique et sulfurique en diffe´rentes proportions. Dans ces milieux, la solubilite´est toujours de type re´trograde et interme´diaire entre celle de´termine´e dans chacun des deux acides. La croissance cristalline re´alise´e dans ce solvant mixte conduita`des cristaux dont la morphologie est elle aussi interme´diairea`celles observe´es dans H 3 PO 4 et H 2 SO 4 . Cette observation montre que lutilisation de me´langes dacide permet de moduler les vitesses de croissance et peuteˆtre un moyen de mieux maiˆtriser celles-ci.

Properties of AT cut gallium phosphate resonators

Abstract Gallium phosphate is a quartz analogue that possesses more intense piezoelectric properties. We report here a study performed to determine more accurately the properties of resonators made using crystal orientations situated near the main cut presenting a zero temperature coefficient at room temperature. Recent crystals having a much improved quality were used to cut plano-convexe resonators with five orientations situated in a range of nearly two degrees around the previously determined angular position of this cut. The temperature coefficients of the resonance frequencies of the electrically excited shear modes and the electrical properties of the resonators were determined. The vibration modes were studied using synchrotron radiation X-ray topography. For all the studied cuts, parabolic thermal variations of the resonance frequencies were observed. The temperature of the extremum varies somewhat with the rank of the mode and also, but slowly, with the cut angle. On the whole a very good thermal stability is obtained for the resonators. Q factors higher than those previously measured were obtained together with, as predicted, very interesting values of the equivalent electrical scheme. The observed vibration modes are generally close to those computed using the Tiersten theory. They present several very interesting properties but display several particularities, such as often possessing a second shear component with a noticeable amplitude, which make them somewhat different from the mode of the corresponding quartz resonators.

Piezoelectric and non-linear optical properties of α-quartz type Si1−xGexO2 single crystals

Single crystals of α-quartz type Si1−xGexO2 with x < 0.2 were grown in 0.05 M NaOH solution. Infrared measurements confirmed that crystals grown at high pressure and high temperature have a low –OH group defect content. After a few millimeters of crystal growth under these conditions, α3500 reaches 0.1 cm−1 and no free –OH are present. The d11 value measured on an X-cut from the crystal with x = 0.0375 is 3.08 pC N−1 (±0.15), in good agreement with the value of 2.97 pC N−1 obtained using density functional theory based calculations. Piezoelectric measurements were performed on the Si1−xGexO2 crystal with x = 0.0375, both at room temperature and after annealing at various temperatures. The piezoelectric signal of the crystal with x = 0.0375 and pure SiO2 disappears after annealing at 635 °C and 545 °C, respectively. Nonlinear optical (NLO) properties of Si1−xGexO2 crystals were measured by Makers fringe technique on Z-cut χ11(2) and their corresponding values for x = 0.023 and 0.028 are 1.3(2) pm V−1 and 1.6(2) pm V−1, respectively. These values are in good agreement with density functional theory based calculations. The light induced damage threshold values measured on Si1−xGexO2 crystals with x = 0.023 and 0.028 are very similar to that of α-quartz.