Gallium Phosphate Research Articles

Negative Thermal Expansion in the Aluminum and Gallium Phosphate Zeotypes with CHA and AEI Structure types

We present a high-resolution powder X-ray diffraction study as a function of temperature of three structurally related, open-framework phosphates: AlPO4 and GaPO4 with the CHA-type structure (AlPO-34 and GaPO-34, respectively) and AlPO4 with the AEI-type framework (AlPO-18). On the basis of refined lattice parameters (in space group R3 for the CHA materials and Cmcm for AEI) all three materials show negative thermal expansion. In the case of AlPO-34, this is found from 110 to 450 K; for GaPO-34, the volume expansion is net negative above 210 K, below which there is a phase transition to a new monoclinic polymorph. For AlPO-18, the behavior of the negative thermal expansion (110−450 K) can be related directly to AlPO-34 by using polar plots in certain specific crystallographic planes that imply that certain common structural features are responsible for the behavior. We compare the results with published data for SiO2 with the CHA-type structure; this shows that the isoelectronic AlPO4 has rather similar ...

Electromechanical properties and defect chemistry of high-temperature piezoelectric materials

Langasite and gallium phosphate are shown to exhibit piezoelectrically stimulated bulk acoustic waves up to at least 1,400 and 900 °C, respectively. Most critical issues are stoichiometry changes due to, e.g. low oxygen partial pressures, and high losses. Therefore, the paper discusses the atomistic transport and defect chemistry of those crystals and correlates them with the electromechanical properties. First, the defect chemistry of langasite is investigated. As long as the atmosphere is nearly hydrogen-free, the transport of charge carriers is governed by oxygen movement. A dominant role of hydrogen is observed in hydrogenous atmospheres. Based on the developed defect model, donors are expected to suppress the oxygen vacancy concentration and, thereby, the loss in langasite. The prediction is proven by niobium doping and found to be valid. A one-dimensional physical model of thickness shear mode resonators is summarized. The analysis of the resonance spectra showed that the loss of the resonators can be described satisfactorily by mechanical and electrical contributions expressed as effective viscosity and bulk conductivity, respectively. The mechanical loss in langasite is significantly impacted by the electrical conductivity due to the piezoelectric coupling. The effect of the piezoelectric coupling on the loss is negligible for gallium phosphate since it shows an extremely low electrical conductivity.

Ionothermal synthesis of microporous aluminum and gallium phosphates

Four aluminum and gallium phosphates including AlPO 4-quartz ( 1), GaPO 4-quartz ( 2), AlPO 4-LTA ( 3) and GaPO 4-LTA ( 4) were ionothermally synthesized using [Emim]Br as structure-directing agent (SDA) and solvent. The samples were characterized by scanning electron micrographs (SEM), X-ray single crystal diffraction and X-ray powder diffraction (XRD). Effects of synthesis conditions, such as P 2O 5/Al 2O 3 and HF/Al 2O 3 ratios, as well as P 2O 5/Ga 2O 3 ratio and reaction temperature on the crystallization of aluminum and gallium phosphates were investigated, respectively. It was indicated that the P 2O 5/Al 2O 3 ratio or P 2O 5/Ga 2O 3 ratio played the dominant role in the phase transformation of aluminum phosphates or gallium phosphates.

High pressure raman spectroscopic study of low-cristobalite GaPO4

Gallium orthophosphate of low-cristobalite structure has been studied by Raman spectroscopy up to 28.5 GPa. Three phase transitions have been identified: 1.6, 3.1 and ∼7 GPa. Raman spectra (200 to 700 cm-1) acquired above 3 GPa show signs of six-coordinated gallium ions, in agreement with earlier studies that the orthorhombic C2221 structure transforms into the orthorhombic Cmcm structure. As pressure increases above 8 GPa, the Raman peaks associated with the low-cristobalite framework structure diminish gradually and replaced by peaks that are possibly related to isolated phosphate units. The spectra also show that the structure of the quenched sample retains that of the high-pressure phase prior to decompression.

Effect of Gallium Oxide on Phase Assemblage in Apatite and Whitlockite Hosts for Waste Immobilization

AbstractTo immobilize halide and actinide ions present in specific ILW waste a process has been developed that uses mineral phases as the host material. The mechanism of substitution of gallium into these phases will have a large effect on the phase assemblage. This will inevitably affect the total amount of halide that can be immobilized in to total phase mixture.The full simulated waste stream composition containing varying concentrations (1–40 wt.%) of gallium oxide was studied. Also nominal compositions for gallium doped fluorapatites (Ca10-1.5xGax)F2(PO4)6 (x = 0, 0.25, 0.5, 0.75, 1.0) and gallium doped whitlockites Ca9Gay(PO4)6+y (x = 0.2, 0.4, 0.6, 0.8, 1.0) were prepared at 750–1050 °C.These were studied by powder x-ray diffraction (XRD) to determine the phase assemblage and solid solution limits of gallium in the apatite and whitlockite phases. It was found that a complete solid solution was formed between whitlockite, Ca3(PO4)2, and Ca9Gay(PO4)6+y. In the nominal apatite compositions it was found that gallium did not substitute into the apatite structure but was instead partitioned over Ca9Gay(PO4)6+y, gallium phosphate, and unreacted gallium oxide. At higher temperatures gallium suppressed the formation of the apatite phase and was largely partitioned into the Ca9Gay(PO4)6+y phase whereas at lower temperature the majority was present as unreacted Ga2O3. In the full DCHP compositions it was found that gallium is likely to be partitioned over a number of phases including apatite, cationdoped whitlockite and gallium phosphate.

Elastic characterizations of α-GaPO4 single crystals grown by the flux method

Transparent gallium orthophosphate single crystals with theα-quartz-typestructure, α-GaPO4, were obtained using the high temperature solution growth technique in aLi2O–3MoO3 flux. A first measurement of several elastic constantsCijkl of themillimeter-size α-GaPO4 piezoelectric single crystals obtained is reported. The elastic constants were computed fromthe resonance frequencies of the thickness vibration modes measured, at room temperature,in plates polished in these crystals. These resonances were excited either by an electric fieldnormal to the plates (conventional thickness excitation) or by a field parallel tothe surface of the plates (lateral field excitation). As usual, the elastic constantswere extracted using the formulae given by the corresponding one-dimensionaltheories of thickness vibration of piezoelectric plates. The measured elastic constantsCijkl of theflux-grown α-GaPO4 were generally found to be higher than those measured withα-GaPO4 crystals grown using the hydrothermal technique. This is most probably related to theextremely weak concentration of OH impurities existing in the crystals obtained using thisflux-growth method.

Ionothermal Synthesis and Characterization of a Layered Propylene Diammonium Gallium Phosphate, (C3H12N2)6[Ga12P16O64] · 4.3 H2O

AbstractA new propylene‐1,3‐diammonium gallium phosphate of composition (C3H12N2)6[Ga12P16O64] · 4.3 H2O (LUH‐1) was obtained by ionothermal synthesis using a deep‐eutectic solvent (DES) composed of choline chloride and tetrahydro‐2‐pyrimidione as reaction medium. The structure‐directing agent propylene‐1,3‐diammonium was generated in situ by the thermally induced decomposition of the amide component of the DES. Single‐crystal X‐ray structure analysis revealed that LUH‐1 is built from macroanionic tetrahedral gallium phosphate layers and layers of interlamellar propylene‐1,3‐diammonium cations, with the latter exhibiting two‐fold disorder. The one‐dimensional 12‐membered ring channel system is occupied by highly disordered water molecules. As indicated by thermogravimetry and powder X‐ray diffraction the water molecules can be desorbed from LUH‐1 at ca. 100 °C with retention of the layered inorganic‐organic hybrid structure. Crystal data for LUH‐1: Trigonal system, space group $P{\bar 3}$ c1 (No. 165), Z = 1, a = 12.905(4), c = 18.317(8) Å, T = 297 K.

Design of high frequency GaPO4 BAW resonators by chemical etching

Abstract GaPO 4 is a piezoelectric quartz homeotype material. For bulk acoustic waves device application, chemical etching is used to obtain very thin piezoelectric membranes. This paper presents a way to design high frequency resonators by chemical etching. Before etching, GaPO 4 samples were characterized by X-ray diffraction topography and infrared absorption spectroscopy to evaluate the dislocation and –OH content, respectively. The chemical etching of gallium orthophosphate in H 3 PO 4 and NH 3 based solvents are compared. The anisotropy of the etching was studied using four different crystalline orientations. For the crystalline orientation used in electronic applications (AT cut), mixed H 3 PO 4 –GaPO 4 solutions are not suitable because they produce major surface defects for etching depths above 40 μm. For the etching of this orientation, basic (NH 3 –K 3 PO 4 ) solutions were preferred as they appear to allow to dissolve, without major defects, depths of up to 250 μm. The measurement of the resulting roughness either with a profilometer or by AFM gives a roughness of 0.02 μm r.m.s. without generating important surface defects. The piezoelectric properties of the etched plates were measured by the air-gap method as a function of the etching depth. No modification of the quality factor Q was observed for depths up to 200 μm. A three-dimensional etching process, involving a mechanical mask, was developed in order to manufacture AT antimesa resonators. Up to now, according to the raw material quality, the highest frequency obtained for the fundamental mode is 26.5 MHz ( QF = 1.1 × 10 12 ) and 16.5 MHz ( QF = 1.6 × 10 11 ) after 88 μm and 150 μm etching depths in H 3 PO 4 + GaPO 4 and NH 3 + K 3 PO 4 solvents, respectively.

Characterizations of piezoelectric GaPO4 single crystals grown by the flux method

Hexagonal gallium orthophosphate crystals have been obtained by spontaneous nucleation using the slow cooling method from X2O–3MoO3 fluxes with X=Li, K. Compared to GaPO4 crystals grown by hydrothermal methods, infrared measurements have revealed flux-grown samples without hydroxyl groups and thermal analyses have pointed out the total reversibility of the phase transition α-quartz GaPO4↔β-cristobalite GaPO4. The elastic constants of these millimeter-size flux-grown α-GaPO4 piezoelectric crystals were experimentally determined from their Brillouin scattering behaviour at room and high temperatures. The room temperature results were in good agreement with the published ones concerning hydrothermally grown samples and the two longitudinal elastic constants measured versus temperature until 850 °C have shown a monotonous evolution.

Control of framework stoichiometry in MeGaPO laumontites using 1-methylimidazole as structure-directing agent

A series of heterometal substituted gallium phosphates, (N 2C 4H 7) 0.5+ x [Me 0.5+ x Ga 2.5− x (PO 4) 3] (Me = Mn, Fe, Co and Zn, x ≈ 0.25), has been synthesised under solvothermal conditions at 433 K in ethylene glycol using 1-methylimidazole as a templating agent and their structures determined at 150 K using single-crystal X-ray diffraction. The compounds are isostructural, crystallising in the monoclinic space group C 2/ c, with lattice parameters ca. 15 × 13 × 15 Å and β = 112 °, and adopt the laumontite framework type (LAU). The incorporation of 1-methylimidazole cations into the one-dimensional pore systems of these materials is about three quarters the uptake value obtained previously for the less-bulky amine cations of imidazole and pyridine in other MeGaPO laumontites, which have the formula (TH)[MeGa 2(PO 4) 3] (Me = Mn, Fe, Co and Zn; T = C 5H 5N and C 3N 2H 4). The size, shape and charge of the amine clearly influence both the metal-phosphate framework stoichiometry (i.e. Me 2+:Ga 3+ ratio) and the framework charge.

An unusual hydrothermal phase transformation of quartz-type gallium phosphate into zeotype GaPO 4-LTA and backwards

An unusual hydrothermal phase transformation of quartz-type gallium phosphate into zeotype GaPO 4-LTA and backwards

Jasminaldehyde Synthesis Catalyzed by Al(Ga)PON Oxynitrides: Influence of the Reaction Conditions

Nitridation of amorphous aluminium phosphate (AlPO4) and mixed aluminium gallium phosphate (Al0.5Ga0.5PO4) under ammonia flow allows preparing “AlPON” and “AlGaPON” bifunctional acid-base heterogeneous catalysts. Their acid-base bi-functional character allows their use as selective catalysts for the production of jasminaldehyde through the cross-condensation of heptanal and benzaldehyde, followed by the dehydration of the aldol intermediate product. Three parameters enabling to maximize the jasminaldehyde yields in a batch reactor operated at 125°C were investigated: the catalyst composition (Al/Ga and O/N ratio), the reactant concentration and the amount of catalyst in the reactor. Maximum jasminaldehyde selectivities were obtained for intermediate nitrogen contents (7-10 wt.%). Maximum reaction rates were obtained using pure reactants and a catalysts weight equal to 10% of the total reagent weight.

Picosecond mid-IR laser induced surface damage on Gallium Phosphate (GaP) and Calcium Fluoride(CaF2)

Picosecond mid-IR USPL induced surface damage on a Gallium Phosphate (GaP) and Calcium Fluoride (CaF₂) is reported. A semiconductor GaP and a dielectric material CaF₂, that are transparent over 3~10 ㎛, were exposed to one picosecond mid-IR light (4.7 ㎛) to investigate laser-induced surface morphological changes on the target. The initiation of damage along the polishing scratch line of GaP and the random location of damage digs on the CaF₂ suggests that the mid-IR picosecond laser-induced damage on targets started from intrinsic surface defects. Multiple pulse irradiations produced periodic corrugated surface structures (ripples) perpendicular to the polarization of light on both GaP and CaF₂. In terms of the orientation and the spacing between ripples, observed ripples have common features with previously reported ripples.

Simple operated multipurpose temperature control cryostat

A suitable simple optical cryostat for optical, magneto-optical, electrical and thermo-electrical measurements was designed. It is suitable for use in a magnetic pool gap as narrow as less than 1 cm. Throughout a long period of time, the heat diffusion process of the cryostat can be easily operated at slow increase in sample temperature in a range 1.25 K/min at 200 K that will be reduced gradually to 0.66 K at room temperature. Liquid nitrogen was used to cool down the temperature. During the operation, the change in the measured energy gap of a semiconductor sample and other physical parameters resulting from the change of temperature can be corrected through the temperature coefficient of that parameter at the corresponding temperature. The cryostat was successfully used for all experiments mentioned above to measure the properties of a single crystal of GaP (Gallium Phosphate) semiconductor.

The structural influence of chromium ions in lead gallium phosphate glasses by means of spectroscopic studies

PbO–Ga2O3–P2O5 glasses containing different concentrations of Cr2O3 ranging from 0 to 1.0mol% were prepared. A number of studies viz., differential thermal analysis, infrared, optical absorption, ESR and Raman spectra of these glasses have been carried out as a function of chromium ion concentration. The analysis of the results of these studies indicated that chromium ions mostly exist in Cr3+ state in these glasses when the concentration of Cr2O3⩽0.4mol% occupy octahedral positions and above this concentration chromium ions seem to subsist in Cr6+ state and occupy tetrahedral positions with CrO42- structural units.

Thermal compensation in GaPO4 beam resonators: experimental evidence for length extensional mode

Temperature effects in gallium orthophosphate (GaPO4) vibrating beams are reported. In addition to the well-known, thickness-shear AT-cut, temperature-compensated cuts exist in GaPO4 for length extensional modes. Experimental evidence of a temperature-compensated cut in GaPO4 rectangular beam resonator vibrating in length extension is given.

Morphology evolution of GaPO4 mesocrystals in a nonionic triblock copolymer system by pH-dependent control

In the synthesis of gallium phosphate, GaPO4, crystals via a hydrothermal route, using amphiphilic triblock copolymer F127, [(EO)106(PO)70(EO)106]–OH, as a surfactant-template, a pH-dependent morphology evolution is observed in the progress of crystal growth. By altering the initial pH level from 7.34 to 11.54, the morphology of crystals is varied from the mesoscale assembly of nanoparticles with porosity, so-called porous mesocrystals, to colloidal crystalline nanoparticles. Thus far, the porous GaPO4 mesocrystals created by self-assembled nanoparticles, is reported for the first time. The typical pore size distribution of porous GaPO4 mesocrystals derived from the adsorption branch by the Barrett–Joyner–Halenda (BJH) model ranges from 1.0 to 3.5 nm with a major distribution peak centered at 2.5 nm.

Growth and thermal stability of GaPO4 epitaxial thin films

Thin epitaxial films of gallium orthophosphate (GaPO4) are grown on α-quartz (SiO2) substrates. Here, amorphous stoichiometric precursor layers fabricated by pulsed-laser deposition on (001) SiO2 substrates are transformed to crystalline GaPO4 by postannealing in air at 650–950°C. Epitaxial films with thicknesses up to 300nm exhibit strong in-plane and out-of-plane textures (angular widths <0.6°). Long-term annealing in air at temperatures above the α- to β-phase transition of the quartz substrate (573°C) does not degrade the films.

High temperature piezoelectric materials: Defect chemistry and electro-mechanical properties

Langasite (La 3 Ga 5 SiO 14 , LGS) and gallium orthophosphate (GaPO 4 ) resonators exhibit piezoelectrically exited bulk acoustic waves at temperatures of up to at least 1400°C and 900°C, respectively. Their mass sensitivity at elevated temperatures has been found to be about as high as that of quartz at room temperature. Within its operation temperature range, GaPO 4 shows significantly lower losses than LGS. Factors restricting application relevant properties of LGS at elevated temperatures, such as the mass resolution, include excessive viscous damping. Therefore, the effective viscosity is determined as a function of the temperature by fitting the calculated complex impedance to the experimental data in the vicinity of the resonance frequency. The viscosity shows an Arrhenius-like behavior if a temperature independent contribution is subtracted. The activation energies of the viscosity for LGS and GaPO 4 correspond to those of the bulk electrical conductivity for each material. Viscosity and conductivity are obviously correlated. Therefore, it is highly likely that the predominant conductivity mechanism also controls the mechanical damping. First attempts to minimize the viscosity of LGS by doping are undertaken. Very light doping does, however, not change the conductivity and viscosity of LGS. Higher doping levels have to be applied and tested. Based on the electromechanical properties given for un-doped LGS, the applicability of this material as resonant gas sensor at 600°C is demonstrated.

High-temperature 434 MHz surface acoustic wave devices based on GaPO/sub 4/

Research into surface acoustic wave (SAW) devices began in the early 1970s and led to the development of high performance, small size, and high reproducibility devices. Much research has now been done on the application of such devices to consumer electronics, process monitoring, and communication systems. The use of novel materials, such as gallium phosphate (GaPO4), extends the operating temperature of the elements. SAW devices based on this material operating at 434 MHz and up 800 degrees C, can be used for passive wireless sensor applications. Interdigital transducer (IDT) devices with platinum/zirconium metallization and 1.4 microm finger-gap ratio of 1:1 have been fabricated using direct write e-beam lithography and a lift-off process. The performance and long-term stability of these devices has been studied, and the results are reported in this paper.