High-temperature X-ray Diffractometry Research Articles

Scalable method for the preparation of CoxNi1-x/alumina nanocomposites and their magnetic heating properties

Magnetic nanocomposites with a high surface area matrix are attractive materials for novel catalyst supports. They can be remotely and selectively heated inside the reactor vessel when exposed to a high-frequency alternating magnetic field (AMF). These so-called "magnetic" or "cold" catalysts can revolutionize the chemical industry's electrification, particularly for renewable energy applications such as hydrogen storage and release. In this study, we developed a scalable method for synthesizing magnetic CoxNi1-x-Al2O3 nanocomposites. The synthesis is based on the co-precipitation of Co and Ni ions from an aqueous solution, coating the precipitated nanoparticles with a boehmite (AlOOH) shell via the in-situ hydrolysis of AlN powder and reduction at 850 °C in a flow of H2. A combination of X-ray diffractometry (XRD) and scanning transmission electron microscopy (STEM/EDXS) showed the formation of nanocomposites containing globular CoxNi1-x nanoparticles (∼ 14 nm in size), homogenously distributed within the matrix composed of thin γ-Al2O3 nanosheets (∼ 30 nm wide and up to 3 nm thick), providing a high specific surface area (∼ 140 m2 g−1). The reduction process was studied using high-temperature XRD, hydrogen-temperature programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The magnetic properties were measured with a vibrating-sample magnetometer (VSM). The nanocomposites exhibited an excellent heating ability, exceeding 800 °C within a few minutes, even at relatively low AMF amplitudes (up to 58 mT) in a fixed-bed reactor. These results underscore the potential of CoxNi1-x-Al2O3 nanocomposites for high-temperature catalytic processes, marking an advancement in magnetic catalyst support synthesis.

Pyrolysis of folic acid: Identification of gaseous/volatile products and structural evolution of N-doped graphitic carbon

Folic acid (FA) is a low-cost and suitable source for producing different N-doped carbon materials by pyrolysis. However, the pyrolytic steps of FA are not entirely understood, particularly above 350 °C, which hampers the intelligent design of tailor-made carbon materials by a one-pot route. In this work, the pyrolytic decomposition steps of FA were investigated by simultaneous thermogravimetric analysis (TGA) and differential scanning calorimetry (TGA-DSC). The released gaseous/volatile products were probed by coupling TGA to infrared spectroscopy and mass spectrometry (TGA-FTIR-MS). Considering the thermal analysis data, FA was pyrolysed in a furnace at 350, 430, 570, 800, and 1000 °C, and the products were analysed by X-ray diffractometry (XRD), vibrational spectroscopy, and X-ray photoelectron spectroscopy. In situ high-temperature X-ray diffractometry (HT-XRD) experiments were also conducted under the nitrogen atmosphere. According to the data set, insights about FA decomposition steps could be proposed, including gaseous/volatile products released during the process and the structural evolution of N-doped graphitic carbon. The formation of carbonaceous material initiated between 200 and 350 °C through polymerisation/condensation reactions, and this step was marked by the release of 2-pyrrolidone and aniline. The graphitisation was enhanced above 350 °C, increasing graphitic nitrogen while the amide groups vanished. The process was accompanied by deoxygenation (i.e., CO and CO2 release) and denitrogenation (e.g., NH3, HNCO, and HCN) reactions. In the 570–800 °C range, the N-enrichment of carbon material (N-pyridine, N-pyrrole/Csp2-N in 5,7-membered rings, and nitrile) could occur by the reaction of released NH3 over the char surface. Graphitic-like structures containing mainly N-graphite and N-pyridine were obtained above 800 °C. The original data about the thermal decomposition steps of FA allow for optimising the synthesis of N-doped carbon materials suitable for applications in adsorption, sensing, catalysis, and energy storage.

Study on the mechanical properties, microstructure and hydration mechanism of phosphogypsum-based geopolymer cement with added micron-sized silica particles

Phosphogypsum (PG) is a solid waste product that is generated during the manufacture of phosphoric acid. In this study, beta-hemihydrate phosphogypsum (β-HPG), slag, sodium metasilicate (SM), citric acid (CA) and micron-sized silica particles (MSSP) were mixed to form a phosphogypsum-based geopolymer (PBG) cement. The results revealed that by adding 3 % MSSP, the 28-day unconfined compressive strength (UCS) reached its highest level of 59.2 MPa. Furthermore, adding 2 % MSSP resulted in the greatest water resistance, with a softening coefficient of 0.92. Additionally, X-ray diffractometry (XRD) Rietveld analysis, scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) imaging, thermogravimetry-differential scanning calorimetry (TG-DSC) analysis, high-temperature XRD analysis, and mercury intrusion porosimetry (MIP) testing were employed to analyse the PBG cement. Results indicated that dihydrate gypsum (CaSO4·2H2O), ettringite (Ca6(Al(OH)6)2(SO4)3(H2O)26), and polymers (Nan{−(SiO2)zAlO2}n·ωH2O) were the principal hydration products in the PBG cement system. Also, the addition of MSSP led to reduced porosity, lower pore-specific surface area, and fewer cracks in the cement structure. After exceeding temperatures of 990.9 °C, these polymers gradually decomposed into Na6(AlSiO4)6, Al2O3, and SiO2. PBG cement is characterized by its easy processing, high strength, eco-friendly nature, and high PG incorporation. It shows promise as a potential substitute for traditional Portland cement in certain sectors, thereby facilitating the consumption of waste gypsum.

Stabilization of hercynite structure at elevated temperatures by Mg substitution

Hercynite, FeAl2O4, is a spinel applied in various fields, including refractory materials or H2 production. FeAl2O4 is unstable at elevated temperatures of 1000 °C in air, decomposing into different forms of alumina and iron oxides. In this work, we show that it is possible to inhibit this decomposition by the substitution of Fex+ in tetrahedral sites of hercynite by Mg2+. Spinel series, Fe1-xMgxAl2O4 (x=0,0.3,0.5,0.7), were prepared using arc plasma melting technique to obtain high-purity and dense materials. The composition Fe0.7Mg0.3Al2O4 was subjected to further in-depth high-temperature in situ investigation of stability using High-Temperature X-Ray Diffractometry up to 1200 °C in air. Also, isothermal oxidation was conducted in the same conditions on both powdered and bulk samples, followed by subjecting the oxidized samples to structural analysis by X-Ray Diffractometry, Mössbauer Spectroscopy and X-Ray Absorption Spectroscopy using synchrotron radiation. The microstructure of oxidized bulk samples was analyzed by SEM/EDS. Mg substitution in hercynite was found to sluggish the spinel oxidation and decomposition. Magnesioferrite inverse spinel formation was found as responsible for, stabilizing the structure up to 1200 °C in air.

Experimental study and thermochemical assessment of the reciprocal system Li+, K+//Cl−, CO32−

In this work a new thermodynamic dataset of the reciprocal system Li+, K+//Cl−, CO32− was generated by using Calphad method with FactSage. After collecting and analyzing the available thermodynamic data in the literature, experiments were designed to improve the comprehensiveness of the new database. Specifically, Differential Thermal Analysis (DTA) was used (1) to confirm the eutectic temperature of the K2CO3–KCl system, (2) to check the solid solubility in the K2CO3–Li2CO3 system and (3) to measure the phase equilibria of the diagonal sections (i.e. Li2CO3–(KCl)2 and K2CO3–(LiCl)2) in the reciprocal system. In addition, the heat capacity of the intermediate compound LiKCO3 was measured by three types of Differential Scanning Calorimetry (DSC) and its phase transformation was studied by High temperature X-ray Diffractometry (HTXRD). Based on the literature data and the present experimental results, the thermodynamic data on pure LiCl, all sub-binary systems and the reciprocal system were reassessed in the new database, which can be used to calculate and predict the thermodynamic properties of the salt mixtures in the reciprocal system Li+, K+//Cl−, CO32− more precisely and reliably.

Thermal expansion, crystal structure, XPS and NEXAFS spectra of Fe-doped bismuth tantalate pyrochlore

The thermal behavior, crystal structure and charge state of ions in the composition of a new pyrochlore Bi1.6Fe0.8Ta1.6O7.6 (refined formula Bi1.50Fe0.60Ta1.40O6.77) synthesized via standard ceramic method are studied. The disordered pyrochlore structural parameters were obtained by the Rietveld method (sp. gr. Fd-3m:2 (227), 10.49689(3) Å, Z = 8). Iron (III) ions occupy octahedral positions of tantalum (V). The sample is characterized by a loose microstructure formed by partially fused grains with a longitudinal size of 0.2–2 μm. Using the high-temperature x-ray diffractometry method it was found that Fe-doped bismuth tantalate pyrochlore is thermally stable up to a temperature of ∼1140 °C. The unit cell parameter a and coefficient of thermal expansion (TEC) uniformly weakly increase from 10.4796 Å to 10.5603 Å and from 4.5 × 10−6 °C−1 to 9.2 × 10−6 °C−1, respectively, in the temperature range of 30 ÷ 1050 °C. This behavior is typical for frame structures of the pyrochlore type. The pyrochlore thermal behavior in the low-temperature region (−170 ÷ 100 °C) is characterized by high growth of TEC from 1.3 × 10−6 °C−1 (−170 °C) to 4.6 × 10−6 °C−1 (100 °C) with respect to a weak increase in a from 10.48627 (−70 °C) to 10.49444 Å(100 °C). According to the data of near edge X-ray absorption fine structure and X-ray photoelectron spectroscopy, the ion charge states were determined as Bi (III), Ta(V), Fe(III).

Thermal expansion of Pb-=SUB=-1-x-=/SUB=-Cd-=SUB=-x-=/SUB=-Te crystals

The values of the lattice period and the linear coefficient of thermal expansion (α) of Pb1-xCdxTe solid solutions are determined depending on the cadmium content and temperature using high-temperature X-ray diffractometry. An increase in the concentration of cadmium in Pb1-xCdxTe in the range x=0.02-0.08 leads to a significant increase in the linear coefficient of thermal expansion. A change in temperature range T=293-673 K leads to decrease in the linear coefficient of thermal expansion. Besides, an increase in temperature does not affect the value α of the undoped PbTe in the indicated temperature range. Keywords: lead telluride, cadmium, solid solutions, lattice period, linear coefficient of thermal expansion.

Structural identification and stabilization of the new high-temperature phases in A(III)–B(VI) systems (A = Ga, In, B = S, Se). Part 1: High-temperature phases in the Ga–S system

This article opens a series of publications devoted to the preparation and stabilization of new high-temperature (HT) semiconductor phases A (III) – B (VI), which have a large number of vacancies and possess a number of unique properties. In this first work from the proposed series, the T-x-diagram of the Ga–S system was investigated in the composition range x = (30.0–60.7) mol% S, and then the structural identification of new HT phases was carried out. For the Ga–S system, four polymorphic (α-, α′-, β-, γ-) Ga2S3 phases of different symmetry were found and displayed on the phase diagram near the Ga2S3 composition (x ∼ 60.0 mol% S). For the first time, it became possible to obtain in-situ a reliable direct proof for the existence of equilibrium in narrow temperature range for the re-opened cubic phase γ-Ga2+δS3 (x ≈ 59.0 mol% S), which was isolated at room temperature in a fairly pure form. We also confirmed the presence of another hexagonal β(α)-Ga2S3 modification, existing at much higher temperatures than the cubic γ-Ga2+δS3 phase. It was shown that the polymorphic α-Ga2S3 and α′-Ga2S3 phases mentioned in the literature form superstructures from the parent β-Ga2S3 phase. The observed structural variants for all four Ga2S3 polymorphic phases, containing up to 1/3 of vacancies in the Ga sub-lattices, are closely related to different methods of ordering Ga vacancies. The reliability of our studies follows from the combination of the methods used: differential thermal analysis (DTA), microstructural local analysis (TEM, HREM, SAED), powder X-ray diffractometry (XRD), including high-temperature synchrotron XRD.

Electrical and Structural Properties of Li1.3Al0.3Ti1.7(PO4)3-Based Ceramics Prepared with the Addition of Li4SiO4.

The currently studied materials considered as potential candidates to be solid electrolytes for Li-ion batteries usually suffer from low total ionic conductivity. One of them, the NASICON-type ceramic of the chemical formula Li1.3Al0.3Ti1.7(PO4)3, seems to be an appropriate material for the modification of its electrical properties due to its high bulk ionic conductivity of the order of 10−3 S∙cm−1. For this purpose, we propose an approach concerning modifying the grain boundary composition towards the higher conducting one. To achieve this goal, Li4SiO4 was selected and added to the LATP base matrix to support Li+ diffusion between the grains. The properties of the Li1.3Al0.3Ti1.7(PO4)3−xLi4SiO4 (0.02 ≤ x ≤ 0.1) system were studied by means of high-temperature X-ray diffractometry (HTXRD); 6Li, 27Al, 29Si, and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR); thermogravimetry (TG); scanning electron microscopy (SEM); and impedance spectroscopy (IS) techniques. Referring to the experimental results, the Li4SiO4 additive material leads to the improvement of the electrical properties and the value of the total ionic conductivity exceeds 10−4 S∙cm−1 in most studied cases. The factors affecting the enhancement of the total ionic conductivity are discussed. The highest value of σtot = 1.4 × 10−4 S∙cm−1 has been obtained for LATP–0.1LSO material sintered at 1000 °C for 6 h.

Thermally Induced Aragonite-Calcite Transformation in Freshwater Pearl: A Mutual Relation with the Thermal Dehydration of Included Water.

This study focuses on the relationship between the aragonite–calcite (A–C) transformation and the thermal dehydration of included water in the biomineralized aragonite construction using freshwater pearl. These thermally induced processes occur in the same temperature region. The thermal dehydration of included water was characterized through thermoanalytical investigations as an overlapping of three dehydration steps. Each dehydration step was separated through kinetic deconvolution analysis, and the kinetic parameters were determined. A single-step behavior of the A–C transformation was evidenced using high-temperature X-ray diffractometry and Fourier transform infrared spectrometry for the heat-treated samples. The kinetics of the A–C transformation was analyzed using the conversion curves under isothermal and linear nonisothermal conditions. The A–C transformation occurred in the corresponding temperature region of the thermal dehydration, ranging from the second half of the second dehydration step to the first half of the third dehydration step. Because the thermal dehydration process is constrained by the contracting geometry kinetics, the movement of the thermal dehydration reaction interface can be a trigger for the A–C transformation. In this scheme, the overall kinetics of the A–C transformation in the biomineralized aragonite construction is regulated by a contracting geometry.

The effects of a Li2O excess on the crystallization sequence of lithium aluminosilicate glass powders

The surface crystallization of melt-quenched lithium aluminosilicate (LAS) glasses with SiO2-contents between 77 and 79 mol% was investigated by high-temperature X-ray diffractometry. Glasses possessing a ratio Li/Al > 1 underwent far earlier crystallization (starting from 750°C) than their stoichiometric counterparts, developing solely quartz solid solution (Qss) and keatite solid solution (Kss) crystals during a heat treatment up to 1200°C. In turn, samples with Li/Al = 1 devitrified only above 900°C and exhibited the transient formation of cristobalite, whose lattice constants hint at a slight Li+Al stuffing. The composition, structural parameters and critical inversion temperature Tc of the obtained Qss crystals were analyzed and compared with the available literature sources, reaffirming the established mutually linear dependence between these properties.

Non-linear Behavior for Chemical Expansion in Yttrium-doped Barium Zirconate upon Hydration

The rates of chemical expansion for 20 at % yttrium-doped barium zirconate upon hydration at 100–900 °C under water partial pressures of 0.008 and 0.023 atm have been studied using combined thermogravimetry and high-temperature X-ray diffractometry. Non-linear behavior for the rates of expansion as a function of proton concentration under equilibrium conditions was observed, suggesting that defect interactions impacted the chemical expansion process.

Тепловое расширение кристаллов Pb-=SUB=-1-x-=/SUB=-Cd-=SUB=-x-=/SUB=-Te

The values of the lattice period and the linear coefficient of thermal expansion (alfa) of Pb1-xCdxTe solid solutions are determined depending on the cadmium content and temperature using high-temperature X-ray diffractometry. Аn increase in the concentration of cadmium in Pb1-xCdxTe in the range x = 0.02–0.08 leads to a significant increase in the linear coefficient of thermal expansion. A change in temperature range T = 293–673 K leads to decrease in the linear coefficient of thermal expansion. Besides, an increase in temperature does not affect the value alfa of the undoped PbTe in the indicated temperature range.

The mechanism of enhanced ionic conductivity in Li1.3Al0.3Ti1.7(PO4)3–(0.75Li2O·0.25B2O3) composites

Abstract The oxide-based Li+ conductors are considered as potential solid electrolytes for lithium-ion batteries. Among the NASICON–type materials, Li1.3Al0.3Ti1.7(PO4)3 (LATP) seems to be a promising candidate for application. Although its bulk conductivity is of the order of 10−3 S · cm−1, and seems to be sufficient for practical use, the total conductivity is considerably limited by the highly resistant grain boundaries. This shortcoming may be overcome by the formation of LATP–based ceramics with appropriate sintering aids. In this study, the 0.75Li2O·0.25B2O3 (LBO) glass with low melting point was chosen to improve the ionic conductivity of LATP. The properties of Li1.3Al0.3Ti1.7(PO4)3–y (0.75Li2O·0.25B2O3) (0 ≤ y ≤ 0.3) system were studied by means of: high temperature X-ray diffractometry (HTXRD), 6Li/7Li, 11B, 27Al and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), thermogravimetry (TG), scanning electron microscopy (SEM), impedance spectroscopy (IS) and density methods. Based on the experimental results, it is shown that the use of LBO glass as a sintering aid results in the enhancement of the total ionic conductivity of LATP ceramics. The correlations between apparent density, microstructure, composition, sintering temperature and ionic conductivity are presented and discussed. The presumed mechanism of the conductivity enhancement is analyzed in terms of the brick-layer model (BLM). The highest value of the total ionic conductivity, equal to 1.9 × 10−4 S · cm−1, was obtained for LATP–0.1LBO sintered at 800 °C.

On the synthesis and structure of the copper-molybdenum oxide bronzes: Monoclinic Cu2Mo10O30 and orthorhombic CuMo9O26

Cu2Mo10O30 was prepared as a monophasic material comprising dark blue platy crystals by reacting Cu with MoO3 under argon at 550 ​°C. Single-crystal X-ray diffractometry showed that Cu2Mo10O30 is a stoichiometric compound that crystallizes with a monoclinic (C2/c) cell: a ​= ​16.6359(6); b ​= ​9.3112(3); c ​= ​27.1597(9) Å; β ​= ​102.621(3)° (Z ​= ​8). Electron paramagnetic resonance spectroscopy revealed that Cu2Mo10O30 displays mixed-valency; (CuI2−xCuIIx)(MoV2+xMoVI8−x)O30 (0 ​≪ ​x ​≤ ​2). Differential scanning calorimetry and in situ high-temperature powder X-ray diffractometry showed that Cu2Mo10O30 decomposes ≳550 ​°C under an inert atmosphere. Dark blue acicular crystals of CuMo9O26 were discovered as a side-product in materials prepared inside evacuated glass ampoules at 500 ​°C. Single-crystal X-ray diffractometry showed these to crystallize with an orthorhombic (Pmmn) cell: a ​= ​3.74190(10); b ​= ​26.4941(4); c ​= ​9.15300(10) Å; (Z ​= ​2). Rietveld refinement of the powder X-ray diffraction data for these materials revealed Cu2Mo10O30 with minor CuMo9O26 and ‘Cu0.1MoO3’.

Advanced technology for in-line continuous heat soak test of tempered sheet glass to guarantee high reliability

Advanced heat soak test (HST) technology, the ‘in-line continuous HST’ has been reported on the basis of experimental investigations and the T-T-T (time–temperature–transformation) relationship. The new HST technology is continuously carried out just after tempering (and heat strengthening) process. It was registered in ISO-20657 (2017). High temperature microscopy observations, high temperature x-ray diffractometry, differential thermal analysis, and micro-Raman spectrometry have been carried out in order to elucidate the α–β phase transformation of nickel sulphide in detail. The breakage ratio of in-line continuous HST is the same as that of conventional off-line HST or excellent. The ‘in-line continuous HST’ is already operating in a Japanese glass plant in order to produce tempered (and heat strengthened) sheet glass with high safety and reliability. The in-line continuous HST technology has the following benefits: (a) improvements of both productivity and reliability, (b) automatic inspection just after the tempering–quenching process, and (c) improvements to productive performance (many kinds products, heteromorphic products, and mass production). In this technical report, the advanced ‘in-line continuous HST’ technology which was standardised by several experimental investigations and analytical results will be shown in detail. The effective and efficient manufacturing technology of the tempered (and heat strengthened) sheet glass will be introduced.

Impact of Li2.9B0.9S0.1O3.1 glass additive on the structure and electrical properties of the LATP-based ceramics

The existing solid electrolytes for lithium ion batteries suffer from low total ionic conductivity, which restricts its usefulness for the lithium-ion battery technology. Among them, the NASICON-based materials, such as Li1.3Al0.3Ti1.7(PO4)3 (LATP) exhibit low total ionic conductivity due to highly resistant grain boundary phase. One of the possible approaches to efficiently enhance their total ionic conductivity is the formation of a composite material. Herein, the Li2.9B0.9S0.1O3.1 glass, called LBSO hereafter, was chosen as an additive material to improve the ionic properties of the ceramic Li1.3Al0.3Ti1.7(PO4)3 base material. The properties of this Li1.3Al0.3Ti1.7(PO4)3–xLi2.9B0.9S0.1O3.1 (0 ≤ x ≤ 0.3) system have been studied by means of high temperature X-ray diffractometry (HTXRD), 7Li, 11B, 27Al and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), thermogravimetry (TG), scanning electron microscopy (SEM), impedance spectroscopy (IS) and density methods. We show here that the introduction of the foreign LBSO phase enhances their electric properties. This study reveals several interesting correlations between the apparent density, the microstructure, the composition, the sintering temperature and the ionic conductivity. Moreover, the electrical properties of the composites will be discussed in the terms of the brick-layer model (BLM). The highest value of σtot = 1.5 × 10−4 S cm−1 has been obtained for LATP–0.1LBSO material sintered at 800 °C.

Thermal and magnetic behavior of BiFeO3 nanoparticles prepared by glycine-nitrate combustion

The temperature behavior of bismuth orthoferrite nanoparticles obtained by the glycine-nitrate combustion method was studied by high-temperature X-ray diffractometry and complex thermal analysis. The region of stability of the material in a single-phase state was found. It was shown that the nanocrystalline BiFeO3 did not undergo decay in the temperature interval 550–780 °С. In this temperature interval, we have obtained the nanocrystalline material with average crystallite sizes 40–90 nm and average particle sizes 100–150 nm the sizes of which depend on temperature. The features of formation of BiFeO3 and the process of their sintering were studied. Results show that the crystallite growth slowed down after the amorphous phase disappeared. The sintering of nanopowder became more intense in the temperature interval 600–700 °С, but no noticeable increase in the crystallite sizes occurred. The magnetic behavior of obtained material was also discussed. It was found to be consistent with the concept of violation of the cycloidal magnetic order in bismuth orthoferrite.

New large-scale production route for synthesis of lithium nickel manganese cobalt oxide

The spray roasting process is recently applied for production of catalysts and single metal oxides. In our study, it was adapted for large-scale manufacturing of a more complex mixed oxide system, in particular symmetric lithium nickel manganese cobalt oxide (LiNi1/3Co1/3Mn1/3O2—NMC), which is already used as cathode material in lithium-ion batteries. An additional lithiation step was coupled with the main process in order to obtain the desired layered structure. Thermogravimetric analysis and high-temperature X-ray diffractometry built the basis for determining suitable synthesis temperature regions for the used chloride precursors and the post-treatment step. The optimized process was proven on an industrial pilot line where a setup for minimum production capacity of 12 kg h−1 was possible. The powder obtained directly after roasting had a very striking morphology compared to the final lithiated product. Hollow aggregates (≥250 μm) with overall 10.926 m2 g−1 surface area and a pore diameter of 3.396 nm were observed. Their well-faceted primary particles were converted into nanosized spheres after lithiation, building a few micrometer big high-porous agglomerates. Actual composition was verified by inductively coupled plasma atomic emission spectroscopy analysis, and the crystal structure and corresponding unit cell parameters were identified and confirmed by Rietveld fit of the derived X-ray diffraction pattern. The initial electrochemical measurements show a 149-mAh g−1discharge capacity, as determined from cyclic voltammetry.

High-temperature stability of the phase composition of langasite family crystals

Thermal stability of the phase composition of langasite family crystals is studied by means of high-temperature X-ray diffractometry upon heating in vacuo and in air. Upon heating above 1000°C in vacuo, the partial decomposition of the initial phase is observed in La3Ga5SiO14, La3Ta0.5Ga5.5O14, and Ca3TaGa3Si2O14 crystals; this is accompanied by the emergence of gallium-depleted oxides of the main elements, due to the formation of volatile gallium protoxide and the loss of gallium in the surface layer of the crystals. Langasite family crystals are found to be stable when annealed in air up to a temperature of 1200°C.