Temperature Dependence Of Lattice Constants Research Articles

Phase Transitions in a Perovskite Thin Film Studied by Environmental In Situ Heating Nano-Beam Electron Diffraction.

The rich phase diagram of bulk Pr1-x Cax MnO3 resulting in a high tunability of physical properties gives rise to various studies related to fundamental research as well as prospective applications of the material. Importantly, as a consequence of strong correlation effects, electronic and lattice degrees of freedom are vigorously coupled. Hence, it is debatable whether such bulk phase diagrams can be transferred to inherently strained epitaxial thin films. In this paper, the structural orthorhombic to pseudo-cubic transition for x= 0.1 is studied in ion-beam sputtered thin films and differences to the respective bulk system are pointed out by employing in situ heating nano-beam electron diffraction to follow the temperature dependence of lattice constants. In addition, it is demonstrated that controlling the environment during heating, that is, preventing oxygen loss, is crucial in order to avoid irreversible structural changes, which is expected to be a general problem of compounds containing volatile elements under non-equilibriumconditions.

Thermodynamic properties of fcc metals using reparameterized MEAM potentials

The modified embedded atom method (MEAM) potentials of Jin et al. (Appl Phys A 120:189, 2015) are reparameterized through fitting the available experimental data and ab initio results of several physical properties better for seven face-centered cubic metals, Ag, Al, Au, Cu, Ni, Pd, and Pt. Results for the structure stabilities, point defects, and phonon dispersion properties are in better agreement with the measured values than those from the original MEAM potentials, showing the reliability of the reparameterized potentials. Also, the thermodynamic properties for these metals are studied within the quasi-harmonic approximation. Calculation results for the temperature dependence of lattice constants, thermal expansion coefficients, molar heat capacities at constant volume and/or constant pressure, isothermal and adiabatic bulk moduli, Gruneisen parameters, and Debye temperatures are compared to those from the earlier embedded atom methods and ab initio method calculations as well as the experimental data.

Ab initio calculations of the thermal properties of boron arsenide

Thermal properties of bulk zinc-blende boron arsenide (BAs) were investigated by performing ab initio calculations using both the local density approximation (LDA) and generalized gradient approximation (GGA) for the exchange-correlation potential. Phonon dispersion relations were studied within the framework of density functional perturbation theory (DFPT) and the subsequent thermal properties were computed using the quasi-harmonic approximation (QHA). We have computed the temperature dependence of lattice constant (ao), isothermal bulk modulus (Bo), linear thermal expansion coefficient (αL), average Grüneisen parameter (γ), and specific heat capacity at constant pressure (CP) as well as at constant volume (CV) of BAs. The calculated LDA values at 300 K of Bo (142.8 GPa), αL (4.01 × 10−1 K−1), γ (0.816), and CP (0.34 J g−1 K−1) are in excellent agreement with the reported experimental values of 148 GPa, 3.85 × 10−6 K−1, 0.82, and 0.4 J g−1 K−1 respectively in the same order. In contrast, the GGA is found to overestimate the values of thermal properties for all the temperatures when compared to LDA, except the isothermal bulk modulus. The discrepancy between the computed LDA and GGA values has been discussed in detail. Results further indicate that the discrepancy between the computed LDA and GGA values of ao,Bo is found to increase with the increase in temperature. In contrast, the discrepancy in the values of CP,CV,γ and αL is found to decrease with the increase in temperature. In the subsequent calculations, the mode-Grüneisen parameter corresponding to various phonon modes has been computed. No negative thermal expansion (NTE) is observed, although, the mode-Grüneisen parameter corresponding to transverse acoustic phonons exhibits a small negative value at the zone-edge of the Brillouin Zone. Finally, the intrinsic lattice thermal conductivity (κℓ) of BAs has been estimated using the Slack’s model. Results indicate that the Slack’s model underestimates the κℓ of BAs, which is possibly due to the low acoustic Debye temperature (θa) obtained for BAs.

Preparation of Structural Phase Diagram of Nd2Ni1-X Cu x O4+δ As New Cathode Materials – Clarification of Existence of Miscibility Gap

Nd2NiO4+δ with K2NiF4 type structure (T-phase) composed of rock salt layer and perovskite layer has attracted much interest as new cathode material for solid oxide fuel cell. It was reported that partial substitution of Cu for Ni-site in Nd2NiO4+δ improved ionic and hole conductivity [1]. However, crystal structure must change depending on Cu content, resulting in possible variation of electrical property, since crystal structure of Nd2CuO4 is T’-phase composed of fluorite layer and [CuO2] sheet, which is completely different from T-phase. For optimization of Cu content in Nd2Ni1-x Cu x O4+δ as cathode material, structural phase diagram between Nd2NiO4+δ and Nd2CuO4+δshould be established. In this study, preparation of Nd2Ni1-x Cu x O4+δ with various compositions was attempted and stability at high temperature was evaluated to establish structural phase diagram. It has been established that there exists miscibility gap in Nd2Ni1-x Cu x O4+δ for 0.4≤x≤0.9 for the first time. Nd2Ni1-x Cu x O4+δ (0.0≤x≤1.0) were prepared by the Pechini method by which preparation of homogeneous specimens can be expected. Nd2O3, Ni(NO3)2·6H2O and CuO powders were dissolved with mixture of dilute HNO3 and H2O2, distilled H2O and dilute HNO3, respectively. They were mixed with nominal composition. After mixing ethylene glycol and citric acid, the mixture was heated at about 450 °C, resulting in precursor. The precursor obtained was calcined at 700 °C for 24 h in air, followed by pressing into pellet and heat-treatment at 1000 – 1200 °C in air for 10 h. For identification of the crystal structure and evaluation of the lattice constants, X-ray diffraction measurement (XRD) was performed. Some XRD patterns were analyzed using the Rietveld analysis employing program RIETAN-FP [2]. Homogeneity of the specimens was evaluated by SEM-EDX analysis (JEOL: JCM-5700 equipped with JED-2300). Temperature dependence of lattice constants and molar volume and existence of the structural phase transition were evaluated using high-temperature X-ray diffraction measurements in the air. XRD patterns at room temperature of Nd2Ni1-x Cu x O4+δ prepared at 1200 °C could be indexed as single orthorhombic T-phase with space group of Fmmm (No. 69) and single tetragonal T-phase with I4/mmm (No.131) for 0.0≤x≤0.1 and 0.2≤x≤0.3, respectively. For diffraction patterns of 0.4≤x≤0.9, peaks assigned as T’-phase were observed in addition to ones indexed as T-phase. With increasing Cu content, intensity of the peaks indexed as T’-phase increased and ones assigned as T-phase decreased. All the peaks of XRD pattern for the specimen with x=1.0, i, e., Nd2CuO4+δ was successfully indexed as tetragonal T'-phase with space group of I4/mmm (No.131). Rietveld analysis revealed that lattice constants and molar volume of both T-phase and T’-phase in the specimens with 0.4≤x≤0.9 were independent on Cu content, indicating existence of miscibility gap for 0.4≤x≤0.9. Also revealed by Rietveld analysis was linear relationship between Cu content and molar ratio of T’-phase which could be ascribed to satisfaction of lever rule in the miscibility gap. EDX image and spectra of Nd2Ni0.4Cu0.6O4+δ depicted in Fig. 1 indicate that two phases with Ni rich and Ni poor composition coexist in the specimen, showing agreement with proposed miscibility gap by Rietveld analysis. High temperature XRD measurements revealed that the miscibility gap for 0.4≤x≤0.9 was maintained up to 1000 °C. For the specimens prepared at 1000 °C, the miscibility gap was observed for 0.3≤x≤0.9, suggesting expansion of the miscibility gap region by decreasing temperature.

Effects of in-plane stiffness and charge transfer on thermal expansion of monolayer transition metal dichalcogenide* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11274280 and 11104254) and the National Basic Research Program of China (Grant No. 2012CB921300).

The temperature dependence of lattice constants is studied by using first-principles calculations to determine the effects of in-plane stiffness and charge transfer on the thermal expansions of monolayer semiconducting transition metal dichalcogenides. Unlike the corresponding bulk material, our simulations show that monolayer MX 2 (M = Mo and W; X = S, Se, and Te) exhibits a negative thermal expansion at low temperatures, induced by the bending modes. The transition from contraction to expansion at higher temperatures is observed. Interestingly, the thermal expansion can be tailored regularly by alteration of the M or X atom. Detailed analysis shows that the positive thermal expansion coefficient is determined mainly by the in-plane stiffness, which can be expressed by a simple relationship. Essentially the regularity of this change can be attributed to the difference in charge transfer between the different elements. These findings should be applicable to other two-dimensional systems.

Development of semi-ab initio interionic potential for CaO and MgO

In this paper, we propose a novel method to derive the interionic potentials for CaO and MgO in conjunction with ab initio calculation and empirical three-body interaction. By using the Chen–Mobius lattice inversion, the pairwise interaction between cations and anions can be evaluated from multiple virtual structures. The quantum-chemistry calculation is carried out to derive the short-range potential for the same species of ions. Empirical three-body interactions are then adopted to heal the drawbacks arising from purely pairwise potential, such as Cauchy relation. The proposed potential is verified by molecular dynamics simulations of some primary properties, including pressure and temperature dependence of lattice constant, elastic constants and phase transition of CaO and MgO. Simulation results are in good agreement with the existing experimental data and ab initio calculations, showing that the developed potentials are valid over a wide range of interionic separations. It is believed that this approach can be readily extended into other materials.

Semi-ab initio interionic potential for gadolinia-doped ceria

In the current work, a set of semi-ab initio interionic pair potentials in a concise functional form with parameters for gadolinia-doped ceria (GDC) systems is derived via the Chen–Mobius lattice inversion and ab initio quantum-chemical calculation. The quality of the proposed potentials is verified by molecular dynamics simulations of CeO 2 and A 2O 3 (A = Ce and Gd) on their static properties, doped concentrations and temperature dependence of lattice constants, mean-square displacements, pair correlation functions and elastic constants. Simulation results are consistent with corresponding experimental data, showing that the new form is valid over a wide range of interionic separations and applicable for describing structural properties of ionic solids.

Structural analysis of Li2TiO3 by synchrotron X-ray diffraction at high temperature

The crystal structure at high temperature and the thermal expansion properties of Li2TiO3, important for use as a tritium breeding material in fusion reactors, have been investigated with high resolution by using high temperature synchrotron X-ray diffraction. The temperature dependence of lattice constants and molar volumes were calculated from the data, and variation of thermal expansion around 450–500°C has been more clearly observed than from high temperature X-ray diffraction using Cu Kα radiation. The variation of thermal expansion can be attributed to existence of a higher order phase transition or appearance of nonlinear thermal expansion.

Larmor diffraction measurement of the temperature dependence of lattice constants in CuGeO3

By using the neutron Larmor diffraction method and a setup based on the improved neutron resonant spin echo option ZETA recently installed on the three-axis spectrometer IN22 (CRG beam line at the ILL), we have determined the precise relative evolution of the inter- and intra-chain lattice constants of the paradigmatic spin-Peierls compound CuGeO3 as a function of temperature. Our results are consistent with previous results obtained by conventional high-resolution diffraction. This method also allows to retrieve independently the sample mosaicities, as well as the widths of various lattice-spacings distributions, thus offering an evaluation of the intrinsic sample quality. In spite of the good definition of the spin-Peierls transition at TSP=14.1(1)K in our sample, we observe a large distribution of lattice constants (Δd/d≃3×10−3), while the mosaicity of the sample appears to be quite reasonable (≲20′).

Analysis of phase transition and expansion behaviour of Al2(WO4)3 by temperature‐regulated X‐ray diffraction

AbstractX‐ray diffraction measurements of Al2(WO4)3 were carried out under various temperatures from 123 K to 373 K. Diffraction patterns above 273 K and below 253 K could be successfully explained as orthorhombic Pbcn (No. 60) and monoclinic P21/n (No. 14) with superstructure, respectively, which were in agreement with the results of convergent‐beam electron diffraction. Thermal expansion of low‐temperature monoclinic phase and slight shrinkage of high‐temperature orthorhombic phase were observed from the temperature dependence of lattice constants and molar volume, showing agreement with the result of dilatometry. It is revealed that abrupt expansion of Al2(WO4)3 at the structural phase transition is attributed to an abrupt increase of the c‐axis, which is parallel to the 21 screw axis and perpendicular to the n‐glide plane. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In situ high temperature XRD studies of ZnO nanopowder prepared via cost effective ultrasonic mist chemical vapour deposition

Ultrasonic mist chemical vapour deposition (UM-CVD) system has been developed to prepare ZnO nanopowder. This is a promising method for large area deposition at low temperature inspite of being simple, inexpensive and safe. The particle size, lattice parameters and crystal structure of ZnO nanopowder are characterized by in situ high temperature X-ray diffraction (XRD). Surface morphology of powder was studied using transmission electron microscopy (TEM) and field emission electron microscope (FESEM). The optical properties are observed using UV-visible spectrophotometer. The influence of high temperature vacuum annealing on XRD pattern is systematically studied. Results of high temperature XRD showed prominent 100, 002 and 101 reflections among which 101 is of highest intensity. With increase in temperature, a systematic shift in peak positions towards lower 2θ values has been observed, which may be due to change in lattice parameters. Temperature dependence of lattice constants under vacuum shows linear increase in their values. Diffraction patterns obtained from TEM are also in agreement with the XRD data. The synthesized powder exhibited the estimated direct bandgap (E g) of 3.43 eV. The optical bandgap calculated from Tauc’s relation and the bandgap calculated from the particle size inferred from XRD were in agreement with each other.

Synthesis and structural characterization of nanostructured copper

In this paper, we report on the preparation and characterization of nanocrystalline powder of copper by dc-magnetron sputtering. Liquid nitrogen cooled cold finger arrangement has been used to prepare nanocrystalline powder. The particle size, crystal structure, and morphology of the samples were characterized by in situ high temperature X-ray diffraction (XRD) and transmission electron microscope (TEM). Results of high temperature XRD showed that highly oriented (111) phase becomes randomly oriented at higher temperature with a systematic shift in peak positions toward lower 2θ values due to changes in lattice parameters. Temperature dependence of lattice constants under vacuum shows linear increase in their values. Diffraction patterns obtained from TEM are also in accordance with the XRD data.

Proton Migration in –N···H···O– Hydrogen-bonded Complex of (Chloranilic Acid)(1,2-Diazine)2 Studied by Dielectric Response and Infrared Absorption Spectra

Abstract A dielectric response by an intermolecular –N···H···O–proton transfer was observed around 120 K for (Chloranilic acid)(1,2-Diazine)2 [CA(1,2-DA)2]. This response, observed on the way of the migration from N–H···O at 300 K to O–H···N below 90 K, was demonstrated by infrared absorption spectra and the temperature dependence of lattice constants.

Magnetic structure, magnetostriction, and magnetic transitions of the Laves-phase compoundNdCo2

The crystal and the magnetic structures as well as magnetostriction of the Laves-phase compound $\mathrm{Nd}{\mathrm{Co}}_{2}$ are investigated by means of temperature-dependent high-resolution neutron-powder diffraction. The compound crystallizes in the cubic Laves phase $C15$ structure at high temperature, undergoes a tetragonal distortion (space group $I{4}_{1}∕amd$) around ${T}_{C}\ensuremath{\approx}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and an orthorhombic distortion (space group $Fddd$) at $T\ensuremath{\approx}42\phantom{\rule{0.3em}{0ex}}K$. The temperature dependence of lattice constants, magnetostriction constant, and magnetic moment indicate that the magnetic and structural transitions are second order in the vicinity of ${T}_{C}$ and are first-order around 42 K. Refinements of magnetic structure reveal that the Nd moment distinctly exhibits an abrupt increase at the first-order transition and the easy magnetization direction of the compound changes from [001] in the tetragonal lattice to [011] in the orthorhombic lattice, indicating a strong coupling between crystal structure and magnetic properties at zero field. Analysis of the temperature dependence of bondlength suggests a strong magnetic exchange striction in the tetragonal structure and that the abrupt increase of the Nd moment is attributed essentially to a change in crystal electric field. Field-dependent neutron diffraction reveals a decoupling of the magnetic and structural transitions under relatively modest magnetic fields.

Fabrications of Pb(Sc1/2Nb1/2)O3/xPbTiO3 Thin Films and Their Structural Characterizations

Highly oriented Pb(Sc1/2Nb1/2)O3 (PSN) and Pb(Sc1/2Nb1/2)O3/43%PbTiO3 (PSN/43%PT) thin films were fabricated on MgO and SrTiO3 (001) substrates by pulsed laser deposition (PLD) technique. La1/2Sr1/2CoO3 was deposited on the substrate as a bottom electrode layer for dielectric measurements. The orientation of the films was checked by X-ray diffraction method, and is found to be well oriented along the c-axis for PSN and PSN/PT. Film thickness was determined by the Laue oscillation of X-ray diffraction profile. This enables us to determine the number of pulses for stacking one layer of PSN and PSN/PT thin films. The temperature dependences of lattice constants of PSN and PSN/PT thin films were determined. They exhibit small but clear changes at almost the same temperature as that of the ferroelectric transition points of PSN and PSN/PT ceramics. The surface roughness of these films was observed using atomic force and scanning electron microscopes. Temperature change of dielectric constant ε and D-E hysteresis loop were determined for PSN and the real part of ε shows 850.

X-Ray Scattering Study of High Temperature Phase Transition of Betaine Phosphate

The I–II phase transition of betaine phosphate crystal associated with the ordering of PO 4 groups has been studied by X-ray scattering: The observations are concerned on (1) the temperature dependence of lattice constants, (2) the temperature dependence of the order parameter of PO 4 which followed the relation η∝( T c - T ) β , β=0.42(1), and (3) the anisotropic distribution of critical diffuse scattering in the reciprocal space above T c ; elongated along the c -direction, shortened along the b * -direction. The critical X-ray diffuse scattering has been analyzed. The correlation lengths along three principal directions of anisotropic scattering distribution were estimated. The temperature dependence of the correlation length and staggered susceptibility were discussed.

Pressure effect and temperature dependence of lattice constants for Ce(Ru0.85Rh0.15)2Si2

Abstract X-ray powder diffraction has been studied on Ce(Ru 0.85 Rh 0.15 ) 2 Si 2 between 300 and 4 K under pressure up to 32 GPa with a diamond anvil cell, and the lattice constants and the bulk modulus have been obtained. The bulk modulus shows a rapid drop between 100 and 50 K , when the temperature decreases from 300 to 4 K . This tendency is most likely attributed to Kondo effect and/or a sign of a spin density wave.

Martensitic transformations, thermal expansion and mechanical properties of titanium-niobium alloys

Thermal expansion in quenched and cold rolled Ti - Nb alloys (30-50 w.% Nb) was studied and temperature ranges were determined, in which anomalies associated with the sample expansion and compression occur. Phase transformations were studied by means of X-ray diffraction in the temperature range -190 < T < +150°C. Cold rolling results in significant decrease of thermal expansion along the rolling direction. Thermal coefficient of linear expansion varies with niobium content for deformed alloys assuming negative values for alloys with 34 - 38 % Nb the minimum value being -1.3.10 -5 K -1 . Anomalies of TCLE are connected to temperature dependences of lattice constants of orthorhombic martensite, volume fractions of the phases and texture of the alloys.

Magnetic phase transition and the corresponding magnetostriction of intermetallic compounds RMn2Ge2 (R=Sm, Gd)

The temperature dependence of lattice constants a and c of intermetallic compounds RMn2Ge2 (R = Sm, Gd) is measured in the temperature range 10-800K by using the x-ray diffraction method. The magnetoelastic anomalies of lattice constants are found at the different kinds of spontaneous magnetic transitions. The transversal and longitudinal magnetostrictions of polycrystalline samples are measured in the pulse magnetic field up to 25T. In the external magnetic field there occurs a first-order field-induced antiferromagnetism-ferromagnetism transition in the Mn sublattice, which gives rise to a large magnetostriction. The magnitude of magnetostrictions is as large as 10-3. The transversal and longitudinal magnetostrictions have the same sign and are almost equal. This indicates that the magnetostriction is isotropic and mainly caused by the interlayer Mn-Mn exchange interaction. The experimental results are explained in the framework of a two-sublattice ferrimagnet with the negative exchange interaction in one of the sublattices by taking into account the lattice constant dependence of interlayer Mn-Mn exchange interaction.

X-Ray Study of Phase Transition in Betaine Phosphite

The phase transition of betaine phosphite crystal associated with the ordering of PO 3 radicals at phase I to II transition has been studied by X-ray scattering: The observations are concerned on (1) the temperature dependence of lattice constants, (2) the temperature dependence of the order parameter of PO 3 which followed the relation η∝( T c - T ) β , β=0.33(1), and (3) the anisotropic distribution of critical diffuse scattering in the reciprocal space above T c ; elongated along the c -direction, shortened along the b * -direction. The critical X-ray diffuse scattering has been analyzed on an Ising model to obtain effective interaction between PO 3 ions. The results are summarized as follows. (1) The correlation lengths along three principal directions of anisotropic scattering distribution was estimated. (2) The temperature dependence of the correlation length follows nearly the mean-field behavior, ξ∝( T - T c ) -ν , ν=0.5.