High-temperature X-ray Diffraction Method Research Articles

The crystal structure and transformations of the omicron phase Ο in the Ti-Al-Nb system and on the ambiguity of its subvariants Ο1 and Ο2

Omicron, Ο-Ti2NbAl alloys have been under continuous development for more than 40 years as potential materials for the gas turbine engine; however, the crystal structure and phase transformations are still unclear. In this work, we clarified the crystal structure, atom positions and phase transformations of the Ο phase by in-situ neutron diffraction and high-temperature X-ray diffraction methods. From room temperature to the vanishing temperature of the Ο phase, the latter exposes a C m c m structure, with Ti and Nb atoms tending to respectively occupy the 8g and 4c2 positions, but with a certain disorder, introducing an order parameter. The phase transformation sequences of Ti-24.8Al-24.3Nb alloy are Ο(975 °C) → βo + Ο(997.5 °C) → βo(1165.5 °C) → β. Moreover, we have proven that a distinction of the omicron subvariants Ο1 and Ο2 is crystallographic nonsense as Ο1 must equal to α2 of P 63/m m c structure, and Ti2NbAl is a prototype structure by itself.

Study of crystallization mechanism of Al-based amorphous alloys by in-situ high temperature X-ray diffraction method

The role of transition metals (TMs) addition on the formation and crystallization of amorphous Al85TMs10Y5 alloys was described using in-situ high-temperature X-ray diffraction. The structural results were compared with differential scanning calorimetry and dynamical mechanical analysis to obtain detailed information about the nucleation and growth of crystalline phases. The performed analysis confirmed that Fe and Cu addition drastically changes the crystallization temperature and the phase composition of the fully crystallized alloys. While for Al85Ni10Y5 alloy, the second crystallization step is related to the formation of Al19Ni5Y3 phase, for Al85(Ni, Fe)10Y5 and Al85(Ni, Fe, Cu)10Y5 alloys crystallization of Al15Fe9Y2 phase was observed. Interestingly, the performed analysis showed that forming a homogenous amorphous phase is not necessary to obtain the best corrosion resistance. It was noted that the precipitation of the YCr2Al20 phase in the Cu-rich amorphous matrix should be a much more interesting approach.

Synthesis and characterization of negative thermal expansion of the Zr2(WO4)(PO4)2 system

In this study, Ti- and Mo-substituted Zr2(WO[Formula: see text](PO[Formula: see text] were synthesized using a conventional solid-state reaction technique. Coefficients of thermal expansions for samples were calculated by the results from the in situ high-temperature X-ray diffraction method. Doping with Ti[Formula: see text] reduces the voids occupied by the thermal vibration ellipsoid perpendicular to the bond axis. On the other hand, by doping Mo[Formula: see text], which has a smaller binding energy with oxygen atoms, thermal vibration in the direction of the bond axis is promoted. It is considered that the average linear thermal expansion coefficient became zero because the elliptical thermal vibration perpendicular to the coupling axis was suppressed by the synergistic effect of the co-doping of Ti and Mo.

Thermal expansion of the nanocrystalline titanium diboride

The research of thermal expansion of nano- and microcrystalline TiB2 in the temperature range of 298–1473 K was carried out by the high-temperature X-ray diffraction method. The grain size effect on the temperature dependence of a and c parameters of TiB2 hexagonal unit cell was established. For nanocrystalline TiB2 with the 5–7 nm coherent scattering region, we found the linear dependence of the metric of the cell on temperature. The thermal expansion coefficient (TEC) of nanocrystalline TiB2 does not depend on temperature and equals 3.58‧10−6 K−1 and 9.92‧10−6 K−1 for the a and c axis respectively. For the microcrystalline TiB2, we detected the nonlinear temperature dependence of unit cell parameter a, which points to the effect of temperature on the coefficient of thermal expansion along a basal plane. The TECa rises from 6.02·10−6 to 9.94·10−6 К−1 in the range of 300–1473 K, while the TECc weakly depends on temperature and remains constant ∼8.38·10−6 К−1, leading to isotropic thermal expansion of microcrystalline TiB2 at 1273–1473 K. The equations which describe the changes of unit cell parameters and coefficients of thermal expansion of nano- and microcrystalline TiB2 as temperature functions are determined.

In-situ thermal phase transition and structural investigation of ferroelectric tetragonal barium titanate nanopowders with pseudo-cubic phase

Optimization and miniaturization of existing electronic devices require the development of advanced nanostructured materials with high phase and structural purity. Over the past decade, barium titanate (BaTiO3) has attracted considerable attention due to its outstanding ferroelectric and dielectric properties. The present study involved the investigation of the phase transition and structural stability of tetragonal BaTiO3 nanopowders with pseudo-cubic phase using an in-situ high resolution and high temperature X-ray diffraction method. Under ambient conditions, the coexistence the tetragonal and cubic phases with weight fractions of 75.7% and 24.3%, respectively, was determined in BaTiO3. In the temperature range of 25 °C-300 °C, phase boundaries of BaTiO3 (180 nm in size) exhibiting several phases were detected. The phase transformation behavior, relative crystal phase content, lattice parameters, crystallite size, and tetragonality of the BaTiO3 nanopowders were established by the Rietveld refinement method at the onset temperature from 25 °C to 300 °C. Up to 150 °C, the nanopowders exhibited a complete transition of the cubic phase. Additionally, a complete tetragonal to cubic transformation was accomplished by a decrease of tetragonality at 125 °C and an increase in the crystallite size at 300 °C.

Thermal expansion and heat capacity of thulium orthotantalate

Monoclinic M′-orthotantalate thulium samples were obtain by co-precipitation and annealing at 1873 K and characterized by X-ray powder diffraction, scanning electron microscopy and chemical analysis. Using the high-temperature X-ray diffraction method, the temperature dependences of the monoclinic lattice parameters were determined at range 298–1273 K and instantaneous βV(i) and relative βV(r) volume expansion coefficients were calculated. The molar heat capacity of M′-TmTaO4 was measured by relaxation (4.1–25.1 K), adiabatic (5.6–348.8 K) and differential scanning (303–1333 K) calorimetry. Standard thermodynamic function (entropy, enthalpy increment and reduced Gibbs energy) were calculated on the smoothed values of molar capacity, without taking into account the contribution of phase transformations occurring below 4 K. The general shape of the anomalous Schottky contribution to the molar heat capacity was determined.

New phase transition in CsPbBr3

Using a combination of in situ high-temperature X-ray diffraction and differential scanning calorimetry methods, the phase behavior of cesium lead bromide CsPbBr3 was investigated in the temperature range of (25–200) °C. In addition to the previously reported Pnma→P4/mbm and P4/mbm→Pm3-m phase transitions, a new fully reversible transition was found to occur between 45 °C and 57 °C. A novel phase, which is stable at least in the temperature range of (57–62) °C, has an orthorhombic structure with Cmcm space group, which makes the sequence of phase transitions upon heating the same for both CsPbBr3 and CsPbCl3 halides: Pnma→Cmcm→P4/mbm→Pm3-m.

Liquid structure of Sn-Ag-xCu solders and its effect on the formation and growth of interfacial Cu6Sn5

The liquid structure of Sn-3.5Ag and Sn-3.5Ag-0.7Cu (wt%) solders was first studied using high-temperature X-ray diffraction method. Only short-range order (SRO) was detected in the liquid Sn-3.5Ag melts. However, besides SRO, medium-range order (MRO) was also detected in the liquid Sn-3.5Ag-0.7Cu melts at 260 °C and 330 °C while not at 400 °C. The MRO structure was considered to be related to Cu6Sn5-type clusters which can stably exist below 330 °C. The parameters of the ordered SRO and MRO clusters were calculated. Then, Sn-3.5Ag-xCu (x = 0, 0.7 and 1.5) solders were reflowed on Cu substrate for different durations to investigate the effect of liquid structure on the formation and growth behavior of interfacial Cu6Sn5 intermetallic compound (IMC). The Cu6Sn5 layers were found to be thicker with higher initial Cu content in the solders. It is proposed that the Cu6Sn5-type MRO clusters provided potential nuclei for the formation of Cu6Sn5, which promoted the IMC growth rate. The difference in liquid structure of the solders was regarded as a key reason for the different IMC growth rate as well as IMC type at the soldering interfaces.

Thermal expansion and thermodynamic properties of gadolinium hafnate ceramics

Gadolinium hafnate samples were obtained by co-precipitation and precursor annealing at a temperature of ~1773 K and characterised by X-ray powder diffraction, scanning electron microscopy and chemical analysis. The molar heat capacity of Gd2Hf2O7 ceramics with a pyrochlore structure was measured by adiabatic (8–340 K) and differential scanning calorimetry (315–1345 K). The heat capacity of gadolinium hafnate was extrapolated to 0 K without taking into account anomalies in the temperature range below 20 K. Standard thermodynamic functions were calculated based on the smoothed values of molar heat capacity: entropy, enthalpy change and reduced Gibbs energy. Using the high-temperature X-ray diffraction method, the temperature dependence of the Gd2Hf2O7 cubic crystal lattice parameter was determined in the range of 298–1273 K and coefficients of instantaneous (αi), relative (αr) and linear thermal expansion (TE) were calculated.

Polymorphic transformations and thermal expansion of some modifications in Ag1.5Cu0.5Se and Ag0.4Cu1.6Se

The Ag[Formula: see text]Cu[Formula: see text]Se and Ag[Formula: see text]Cu[Formula: see text]Se compounds have been synthesized and grown as single crystals. High-temperature X-ray diffraction method was used to study polymorphic transformations. It is shown that the Ag[Formula: see text]Cu[Formula: see text]Se crystals of high-temperature FCC modification are decomposed into Ag2Se and AgCuSe when the temperature decreases below T = 488 K and Ag[Formula: see text]Cu[Formula: see text]Se is decomposed into Cu2Se and AgCuSe when the temperature decreases below T = 540 K. Transformations in both compounds are reversible. Crystalline parameters are obtained and the temperature dependence of the lattice parameters for each phase is built.

Thermal Stability of NaxCrO2 for Rechargeable Sodium Batteries; Studies by High-Temperature Synchrotron X-ray Diffraction.

Thermal stability and phase transition processes of NaCrO2 and Na0.5CrO2 are carefully examined by high-temperature synchrotron X-ray diffraction method. O3-type NaCrO2 shows anisotropic thermal expansion on heating, which is a common character as layered materials, without phase transition in the temperature range of 27-527 °C. In contrast, for the desodiated phase, in-plane distorted P3-type layered oxide (P'3 Na0.5CrO2), phase transition occurs in the following order. Monoclinic distortion associated with Na/vacancy ordering is gradually lost on heating, and its symmetry increases and changes to a rhombohedral lattice at 207 °C. On further heating, phase segregation to two P3 layered metastable phases, which have different interlayer distances (17.0 and 13.5 Å, presumably sodium-rich and sodium-free P3 phases, respectively) are observed on heating to 287-477 °C, but oxygen loss is not observed. Oxygen loss is observed at temperatures only above 500 °C, resulting in the formation of corundum-type Cr2O3 and O3 NaCrO2 as thermodynamically stable phases. From these results, possibility of NaxCrO2 as a positive electrode material for safe rechargeable sodium batteries is also discussed.

Study of the mechanochemical process to crystalline Cu2ZnSnS4 powder

Kesterite-type Cu2ZnSnS4 was synthesized from the corresponding binary sulfides by a mechanochemical route in a planetary ball mill. The reaction progress during this milling step was followed within a time range of 10–180min by powder X-ray diffraction. In addition, the crystallization of the milled material was studied in situ by high-temperature X-ray diffraction methods in the temperature range of 300–500°C. Significant disorder (cation distribution) was observed at 500°C, strongly decreasing during cooling down to ambient temperature with a rate of 60K/h.

High-temperature X-ray diffraction and thermal expansion of nanocrystalline and coarse-crystalline acanthite α-Ag2S and argentite β-Ag2S.

An in situ study of thermal expansion of polymorphic phases of coarse-crystalline and nanocrystalline silver sulfide - monoclinic acanthite α-Ag2S and cubic argentite β-Ag2S - has been carried out for the first time using the high-temperature X-ray diffraction method. The temperature dependencies of the unit cell parameters of acanthite and argentite in the interval of 300-623 K have been determined, and the thermal expansion coefficients of acanthite and argentite have been found. It is shown that the observed difference in the thermal expansion coefficients for nano- and coarse-crystalline acanthite is due to the small particle size of nanocrystalline silver sulfide leading to the growth of anharmonicity of atomic vibrations. It is established by differential thermal analysis that a reversible polymorphic acanthite-argentite phase transformation takes place at ∼449-450 K and the phase transformation enthalpy is equal to ∼3.7-3.9 kJ mol(-1).

Sol-Gel Derived LiNbO<sub>3</sub>: Its Crystallization Behavior Analyzed by High-Temperature X-Ray Diffraction Method

Here, we have examined the crystallization behavior of a sol-gel derived LiNbO3 precursor using a high-temperature X-ray diffraction (HT-XRD) method. LiOC2H5 and Nb (OC2H5)5 were used as starting alkoxides. High-temperature reaction behavior was analyzed by HT-XRD up to 1000°C in air on a Pt stage, as well as by thermogravimetry and differential thermal analysis up to 1100°C in air. HT-XRD, DTA-TG and SEM observation revealed that ~700°C was a favorable temperature to obtain fine and well-crystallized LiNbO3 crystals.

Sol-Gel Derived LiNbO<sub>3</sub>: Its Crystallization Behavior Analyzed by High-Temperature X-Ray Diffraction Method

Here, we have examined the crystallization behavior of a sol-gel derived LiNbO3 precursor using a high-temperature X-ray diffraction (HT-XRD) method. LiOC2H5 and Nb (OC2H5)5 were used as starting alkoxides. High-temperature reaction behavior was analyzed by HT-XRD up to 1000°C in air on a Pt stage, as well as by thermogravimetry and differential thermal analysis up to 1100°C in air. HT-XRD, DTA-TG and SEM observation revealed that ~700°C was a favorable temperature to obtain fine and well-crystallized LiNbO3 crystals.

High-temperature order–disorder phase transition in nacaphite, Na2CaPO4F

The thermal behavior of nacaphite, Na2CaPO4F, was studied by the powder high-temperature X-ray diffraction method. A monoclinic-to-orthorhombic phase transition has been observed at 330 °C associated with the appearance of the Ca/Na disorder at one of the two crystallographically inequivalent Na sites. At room temperature, nacaphite is monoclinic, P21/c, a = 13.3185(14), b = 7.0964(8), c = 10.6490(11) A, β = 113.526(1)°, V = 922.81(17) A3. The structure is based upon one-dimensional antiperovskite units consisting of face-sharing [FNa4Ca2]7+ anion-centered octahedra running parallel to the c axis. The structure is fully ordered and contains two Ca and four Na sites. The crystal structure of the high-temperature modification [refined by Rietveld method (RB 0.025) at 400 °C from the powder X-ray diffraction data] is orthorhombic, Pnma, a = 5.4123(1), b = 7.1196(1), c = 12.3171(1) A, V = 474.62(1) A3. The structure has one fully occupied Na1 site and one mixed occupied Na2 site, the latter being equally occupied by Na and Ca. The Na1 and Na2 sites are coordinated by two F− and four O2− anions each. The phase transition has an order–disorder character and is associated with the decrease of structural complexity measured as an information content per unit cell (300.235 bits for the low- and 98.117 bits for the high-temperature modifications). Thermal expansion of both modifications has an anisotropic character with the degree of anisotropy increasing from the low- to the high-temperature phase. The direction of the strongest thermal expansion is parallel to the direction of chains of face-sharing anion-centered octahedra that can be explained by the temperature-induced expansion of the F–Na/Ca bonds.

Temperature dependence of the inversion degree in three-cation spinel solid solutions: experimental evaluation by XRD

The method of degree of inversion calculation presented in the present paper was based on the determination of several temperature-dependent parameters such as: oxygen positional parameter, lattice parameter, cation site occupancies, and a cation–anion distance in tetrahedral and octahedral sites. The theoretical basis of the method as well as the required derivation of formulae and the conditions of its application has been described.The values of the measured temperature-dependent parameters were used to calculate the degree of inversion vs. temperature in the spinel structure. Initial temperatures of the order–disorder transformation were determined. The described method of investigating the order–disorder phase transformation based on three examples of spinel solid solutions: Mg(Al0.5Fe0.5)2O4, (Mg0.75Ni0.25)Al2O4, and (Mg0.75Co0.25)Al2O4 has been presented. Investigations by means of the high-temperature X-ray diffraction method at temperatures ranging from 25 to 1100 °C were carried out. It has been shown that using the present method, it is possible to determine the distribution of each cation in tetrahedral and octahedral sites at each temperature. In consequence, the unidirectional order–disorder phase transformation as well the bidirectional transformation in the spinel structure can be investigated. The advantages and disadvantages of the method have been discussed and its uncertainties presented.

Low-temperature heat capacity and thermodynamic functions of KTh2(PO4)3

Abstract In the present work temperature dependence of heat capacity of KTh2(PO4)3 has been measured for the first time in the range from 5.5 to 350 K by precision adiabatic vacuum calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity Cp°(T), enthalpy H°(T) − H°(0), entropy S°(T) − S°(0) and Gibbs function G°(T) − H°(0), for the range from T → 0 to 350 K. The value of the fractal dimension D in the function of multifractal generalization of Debye's theory of the heat capacity of solids was estimated and the character of heterodynamics of structure was detected. The high-temperature X-ray diffraction method was used for the determination of thermal expansion coefficients.

Selection of modes for heat treatment of the alloy 21Cr43Ni2Mn2Si2Nb according to high-temperature X-ray diffraction methods

A real-time study of the phase structure of the heat-resistant alloy 21Cr43Ni2Mn2Si2Nb at high temperatures by X-ray diffraction is carried out. The procedure and timing of phase formation in the alloy are determined.

Preparation and structure of BiCrTeO6: A new compound in Bi–Cr–Te–O system. Thermal expansion studies of Cr2TeO6, Bi2TeO6 and BiCrTeO6

A new compound BiCrTeO6 in Bi–Cr–Te–O system was prepared by solid state reaction of Bi2O3, Cr2O3 and H6TeO6 in oxygen and characterized by X-ray diffraction (XRD) method. It could be indexed on a trigonal lattice, with the space group P-31c, unit cell parameters a=5.16268(7)Å and c=9.91861(17)Å. The crystal structure of BiCrTeO6 was determined by Rietveld refinement method using the powder XRD data. Structure shows that there is one distinct site for bismuth (Bi) atom, one chromium rich (Cr/Te=68/32), and one tellurium rich (Te/Cr=68/32) sites, and one distinct site for oxygen (O) atom in the unit cell. All cations in this structure show an octahedral coordination with oxygen atoms at the corners. The thermogravimetric analysis (TGA) of the compound in air shows that it is stable up to 1103K and decomposes thereafter. The thermal expansion behavior of Cr2TeO6, Bi2TeO6 and BiCrTeO6 was studied using High Temperature X-ray diffraction (HTXRD) method from room temperature to 973, 873 and 923K respectively under vacuum of 10−8 atmospheres. All the compounds showed positive thermal expansion with the average volume thermal expansion coefficients of 14.38×10−6/K, 22.0×10−6/K and 16.0×10−6/K respectively.