Dependence Of Lattice Parameter Research Articles

Magnetic phase transition and lattice dynamic features in ErB2C borocarbide

A sample of erbium borocarbide ErB2C was synthesized from a stoichiometric mixture of erbium, boron, and pyrographite hydride. Temperature dependent magnetic susceptibility, heat capacity and lattice parameters of borocarbide at 2–300 K were experimentally investigated, the Raman spectrum was determined and analyzed. Sharp anomalies in the heat capacity and magnetic properties of ErB2C near T = 16.3 K, caused by the transition to the antiferromagnetic state, as well as diffuse anomalies at a higher temperature, caused by the effect of the crystal field (Schottky anomalies) were revealed. It was found that the magnetic phase transition does not cause measurable anomalies in the lattice parameters of borocarbide due to the weak coupling between the Er3+ ion subsystem and the B–C layers. Almost zero thermal expansion of erbium borocarbide in the basal plane (along a and b axes) (anisotropic invar effect) as well as an unusual character of the c-axis thermal expansion were observed. The first of these features is due to the high bonding energy in the B–C layers and the weak bond between the layers in the borocarbide crystal lattice. It was found that the anomalous expansion along the c axis is a consequence of the action of the crystal field. The splitting scheme for the ground level of Er3+ ions by crystal field was determined from the analysis of the Schottky anomaly of the heat capacity.

Structure of plate-shape nanodiamonds synthesized from chloroadamantane—are they still diamonds?

Atomic structure of plate-shaped nanodiamonds synthesized from chloroadamantane was identified with application of large-Q powder diffraction data. Both reciprocal and real space methods of experimental data analysis were applied. Theoretical atomistic models of nanodiamonds were obtained with application of molecular dynamics (MD) simulations. It was found that examined nanodiamond samples with average grain size from 1.2 up to 2.5 nm are plates build from only six hexagonal carbon layers and they are terminated by (111)B surfaces with three dangling bonds. MD simulations showed that as a result of relaxation of surface stresses there appears a complex system of compressive and tensile strains across and parallel to the surface of the plate-nanodiamonds. Identification of the internal structure of nanodiamond was performed based on the analysis of differential interatomic distance diagrams derived from pair distribution functions G(r). Based on MD simulations an atomic model of plate-grains of diamond was elaborated. Usefulness of lattice parameters determined in a routine diffraction data analysis for characterization of nanodiamonds is questioned. As an alternative the application of the apparent lattice parameter is recommended. A dependence of the overall apparent lattice parameter 〈alp〉 on the size and shape of nanodiamond grains terminated by low index crystal faces is presented.

Interface Engineering of Cu(In,Ga)Se2 Solar Cells by Optimizing Cd- and Zn-Chalcogenide Alloys as the Buffer Layer.

The optimization of band alignment at the buffer/absorber interface is realized by tuning compositions of Cd and Zn chalcogenides as the buffer layer toward high-efficiency Cu(In,Ga)Se2 (CIGS) solar cells. Using the special quasi-random structure (SQS) approach, we construct randomly disordered ZnxCd1-xSySe1-y alloys and ZnSxO1-x alloys as alternatives to the traditional CdS buffer layer. The compositional dependence of formation energies, lattice parameters, band-gap energies, and band alignments of ZnxCd1-xSySe1-y and ZnSxO1-x alloys is investigated by first-principles density functional theory calculations. For quaternary ZnxCd1-xSySe1-y alloys, we find that the miscibility temperatures and the bandgap bowing coefficients are proportional to the lattice mismatch between the mixing elements. The linear dependence of lattice parameters, trinomial dependence of band-gap energies and band-edge positions on the alloy-composition of ZnxCd1-xSySe1-y alloys are established. For ZnSxO1-x alloys, we find the lattice parameters also exhibit a linear dependence on its composition. Because of the large lattice mismatch and the chemical disparity between ZnO and ZnS, the bowing coefficient for the bandgap energies of ZnSxO1-x alloys is composition dependent, and is larger for dilute ZnSxO1-x alloys. With the optimization criteria of moderate spike-like conduction band offset, large valance band offset, sufficiently wide bandgap, and lattice match with respect to the CIGS absorber, we illustrate the optimal composition range of both ZnxCd1-xSySe1-y alloys and ZnSxO1-x alloys as the buffer layer of the CIGS solar cells. Our work demonstrates that ZnxCd1-xSySe1-y alloys and ZnSxO1-x alloys are promising buffer layers for high-efficiency CIGS solar cells.

Heat Capacity and Thermal Expansion of M-EuTaO4

This paper presents temperature dependences of lattice parameters in the range 298–1273 K and molar heat capacity in the range 315–1335 K for high-temperature M-EuTaO4 ceramic, which has been characterized by X-ray diffraction, scanning electron microscopy, and chemical analysis.

Growth, crystal structure, and properties of Cu2Cd1-xZnxSnS4 solid solutions

The phase diagram of the Cu2CdSnS4–Cu2ZnSnS4system was constructed using data on differential thermal, X-ray phase and microstructure analysis methods. The diagram can be attributed to the first type according to the Rosebohm classification. The Cu2CdSnS4–Cu2ZnSnS4 solid solution single crystals were grown by chemical vapor transport using iodine as a transport agent. Their structure and unit cell parameters as well as compositional dependences of lattice parameters, pycnometric, X-ray densities and microhardness were determined. It was found that the Vegard's law is fulfilled in solutions studied.

Pressure controlled trimerization for switching of anomalous Hall effect in triangular antiferromagnet Mn3Sn

Here, we present a detailed theoretical and experimental study on the pressure induced switching of anomalous Hall effect (AHE) in the triangular antiferromagnetic (AFM) compound Mn$_3$Sn. Our theoretical model suggests pressure driven significant splitting of the in-plane Mn bond lengths $i.e.$ an effective trimerization, which in turn stabilizes a helical AFM ground state by modifying the inter-plane exchange parameters in the system. We experimentally demonstrate that the AHE in Mn$_3$Sn reduces from 5$\mu\Omega$ cm at ambient pressure to zero at an applied pressure of about 1.5 GPa. Furthermore, our pressure dependent magnetization study reveals that the conventional triangular AFM ground state of Mn$_3$Sn systematically transforms into the helical AFM phase where the symmetry does not support a non-vanishing Berry curvature required for the realization of a finite AHE. The pressure dependent x-ray diffraction (XRD) study rules out any role of structural phase transition in the observed phenomenon. In addition, the temperature dependent in-plane lattice parameter at ambient pressure is found to deviate from the monotonic behavior when the system enters into the helical AFM phase, thereby, supporting the proposed impact of trimerization in controlling the AHE. We believe that the present study makes an important contribution towards understanding the stabilization mechanism of different magnetic ground states in Mn$_3$Sn and related materials for their potential applications pertaining to AHE switching.

Structural and elastic properties of TlInSe2 at high pressure

The results of the structural study of chain-like structured TlInSe2 compound using powder synchrotron X-ray diffraction (XRD) experiments under the pressures up to P = 30.53 GPa and a first principle analysis of structural and elastic properties under the pressures up to P = 50 GPa are reported. The XRD data show the stability of the tetragonal phase in the whole investigated pressure range. Density Functional Theory (DFT) calculations also evidence that at zero pressure the lowest energy structure of TlInSe2 is tetragonal (space symmetry group I4/mcm). At pressures above P ≥ 38 GPa the symmetry of the lowest energy structure changes to face-centered cubic one (Fm-3m). It was shown that the experimentally and theoretically obtained pressure dependences of lattice parameters in tetragonal phase are in good agreement. The pressure dependences of elastic constants, acoustic wave velocities and other elastic parameters, such as bulk modulus, shear modulus, Young's modulus, Poisson's ratio have been calculated.

High Pressure Effect on Structural and Electrochemical Properties of Anionic Redox-Based Lithium Transition Metal Oxides

Summary The richness of anionic redox chemistry in the solid state offers new opportunities and a possible paradigm shift in energy storage. The excess capacity that goes beyond conventional theoretical values is attributed to the anionic redox in Li-rich transition metal oxide cathodes for Li-ion batteries. Their electrochemical behavior is thermodynamically determined by structural evolution. To better understand the electrochemical dependence on structural factors, we have induced structural modifications in pristine and electrochemically activated Li1.144Ni0.136Co0.136Mn0.544O2 through high-pressure treatment. A unique cyclical change of structural reordering is observed in the anionic redox-activated material during operando pressure sweep, characterized by a periodic evolution of superlattice peak intensity in synchrotron X-ray diffraction patterns. During the structural reordering period, the bulk compressibility of the material decreases, even becoming negative. These insights elucidate the structural flexibility and metastability of anionic redox-based materials, which can undergo large compressions and structural modifications while delivering good electrochemical properties.

Structural aspects of pyrochlores stability: influence of the cations in [8]A, [6]B positions and lattice parameters

The influence of mole fraction and nature of the cations in positions [8]A and [6]B of the pyrochlores containing Na+, Ca2+, Cd2+, U4+, Nb5+, Ta5+, Ti4+, Sb5+, Zr4+, V3+, V4+, W5+, W6+ synthesized under hydrothermal conditions at 800 °C, 200 MPa and controlled oxygen fugacity in NaF solution of 1.0 mol·kg−1 H2O on lattice parameters has been considered. The unit cell parameters of the fluorpyrochlores where for Nb5+ or Ta5+ were substituted by other cations showing distinct linear variations from the effective cations radii in positions [8]A and [6]B. Based on the literary data analysis, the two-parameter nonlinear equation describing dependence of pyrochlore lattice parameters on the cation radii for the oxide-pyrochlores has been proposed.

Сравнение спектров поглощения ионов Nd-=SUP=-3+-=/SUP=- в кристаллах NdFe-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-4-=/SUB=-, Nd-=SUB=-0.5-=/SUB=-Gd-=SUB=-0.5-=/SUB=-Fe-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-4-=/SUB=- и Ho-=SUB=-0.75-=/SUB=-Nd-=SUB=-0.25-=/SUB=-Fe-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-4-=/SUB=-

Polarized optical absorption spectra in the range of some f-f transitions of Nd3+ ions in Ho0.75Nd0.25Fe3(BO3)4, Nd0.5Gd0.5Fe3(BO3)4 and NdFe3(BO3)4 crystals were compared at 90 K. Spectral features related to difference of local environment of Nd3+ ions in the mentioned crystals were revealed. In the range of 4I9/2 → 4G5/2 + 2G7/2 transition of Nd3+ ions in Ho0.75Nd0.25Fe3(BO3)4 crystal the appearance of some absorption lines owing to the change of the local symmetry during structural transition R32 → P3121 at ~ 200 K was revealed. Their intensity increases smoothly, when the temperature decreases from the transition point. Temperature dependences of lattice parameters of Ho0.75Nd0.25Fe3(BO3)4 crystal were measured. It was found that at the transition temperature there is a discontinuous change of the lattice parameter a, which indicates a phase transition of the first order. Lattice parameter c changes smoothly.

The lattice parameter – composition relationship of the body centered cubic uranium-niobium alloys

In-situ time-of-flight neutron diffraction experiments were performed on uranium-niobium alloy with 6 wt% Nb to study the lattice parameter-composition relationship for the body centered cubic (bcc) alloys. Based on lattice-parameter measurements of Nb-supersaturated γs phase over the range of 450 – 790 °C, an improved Vegard's-type relationship was established for determination of Nb concentrations at elevated temperatures. Neutron diffraction data were also collected as a function of aging time over the 450 - 600 °C range when γs phase decomposed isothermally into the mixture of orthorhombic α-U and Nb-rich bcc phase, as well as at room-temperature on the alloys aged ex-situ at 500 °C up to five years. From these measurements, the average Nb concentrations in the bcc phase were determined based on the Rietveld refinements of weight fraction and mass conservation relations (lever rule). Over the 15at% – 78at% range of Nb concentrations that correspond to different experimental aging times, the lattice parameters at constant temperatures exhibit a nonlinear S-shaped variation with Nb concentration, and the associated excess volumes of mixing can be described by a subregular solution model of the Redlich–Kister type of polynomial. Over the full range of composition the S-shaped deviation from Vegard's law can be modeled using a combination of an elastic continuum model and a perturbation to the radii of the solute atoms in the solvent, suggesting that electronic interactions between solute and solvent atoms could play an important role in the compositional dependence of lattice parameter for the γ-phase U-Nb alloys. While Vegard's law is a straightforward and reasonably good approximation for the bcc solid solutions in the U-Nb system, the Nb concentrations determined from the weight fraction refinements of diffraction data provide internally consistent, mass-conserving estimates of solute redistribution for the monotectoid reaction.

CePt2Al2: Structural and Bulk Properties.

This work is focused on the structural and physical properties of CePt2Al2, an intermetallic compound. At room temperature, the modulated orthorhombic structure Cmme(a00)000, with = (0.481, 0, 0) has been determined by single-crystal X-ray diffraction supplemented by dependence of lattice parameters above room temperature for which the X-ray powder diffraction was used. The compound undergoes a structural transition to a tetragonal structure above room temperature. This transition exhibits 50 °C hysteresis and creates a domain structure in the sample. The magnetic behavior has been studied by specific heat, magnetization, and transport measurements in the temperature range between 0.5 and 300 K. Specific heat and susceptibility shows an antiferromagnetic order below 2 K. On the basis of electrical resistivity and other bulk measurements, CePt2Al2 can be considered a Kondo lattice material. The presence of a modulated crystal structure opens the possibility of a charge density wave state in CePt2Al2 as observed for (Re)Pt2Si2.

Band-Structure Engineering of ZnxCd1−xSySe1−y Quaternary Alloys as the Window Layer for CdTe Solar Cells

With the optimization of the back contact, improvement of carrier lifetime, and the use of $\mathrm{Se}$-alloyed $\mathrm{Cd}\mathrm{Te}$ as the absorber, the power conversion efficiency (PCE) of $\mathrm{Cd}\mathrm{Te}$ solar cells has now risen beyond 22%. However, further improvement of the PCE of $\mathrm{Cd}\mathrm{Te}$-based solar cells by optimization of the window layer has not been fully discussed. In this work, we propose that ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ alloys can be tuned as promising window layers of both $\mathrm{Cd}\mathrm{Te}$ and ${\mathrm{Cd}\mathrm{Se}}_{x}{\mathrm{Te}}_{1\text{\ensuremath{-}}x}$ solar cells when band alignment and lattice match are taken into account. Using first-principles calculations and the special quasirandom structure approach, we investigate the compositional dependence of formation energies, lattice parameters, band-gap energies, and band alignments of ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ alloys. We find that the interaction parameters and thus the miscibility temperatures of ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ alloys are directly proportional to the lattice mismatch between the mixing elements, and are larger for mixed-cation alloys than for mixed-anion alloys. The lattice parameter of ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ exhibits a linear dependence to its composition. The bowing of band-gap energies of ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ alloys is quite large, due to the symmetry-reduction-induced intraband coupling in quaternary alloys. Finally, we illustrate the optimal composition range of ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ alloys as the window layer for both $\mathrm{Cd}\mathrm{Te}$ solar cells and ${\mathrm{Cd}\mathrm{Se}}_{x}{\mathrm{Te}}_{1\text{\ensuremath{-}}x}$ solar cells. Our work provides a guideline for further improving the performance of $\mathrm{Cd}\mathrm{Te}$ and ${\mathrm{Cd}\mathrm{Se}}_{x}{\mathrm{Te}}_{1\text{\ensuremath{-}}x}$ solar cells by adopting ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ alloys as promising window layers.

Ferromagnetic resonance in nanotwinned Ni–Mn–Ga film undergoing martensitic transformation

The ferromagnetic resonance (FMR) in the shape memory alloys (SMAs) exhibiting structural cubic-tetragonal phase transition has been studied. The influence of instability and spatial inhomogeneity of crystal lattice on the FMR spectra of twinned ferromagnetic SMAs films has been analyzed using statistical model of ferromagnetic martensite. It has been shown that the abnormally strong temperature dependence of lattice parameters of martensitic film gives a noticeable contribution to the temperature dependence of the resonance value of external magnetic field. The narrowing of the resonance peak, which had been experimentally observed on cooling of the film slightly below the Curie temperature, has been explained. It is argued that the martensitic films are good candidates for the experimental study of local elastic strains influence on the shape of the FMR peak.

Effect of electron beam on the crystal structure of nanoscale Al particles

E-beam irradiation is one of the favorite methods of recent years and it can deliver the irradiation dose in just a few seconds to form nanoparticles. It is possible to obtain nanoparticles with different properties by changing the experimental conditions, as well as radiolytic reduction process can be adjusted through accelerators, it is possible to obtain oxides and hydroxides of metal nanoparticles. This paper reports the investigation of high-energy electron beams (EBs) on the crystal structure of 40–60 nm nanoscale Al particles. The crystal structure of the samples was calculated using the Rietveld method in the FullProf program. Structure analysis of three different irradiated ([Formula: see text], [Formula: see text], [Formula: see text]) Al samples and nonirradiated Al samples was performed by XRD. Occurring energy during the process of linear electron acceleration was around [Formula: see text][Formula: see text]2–3 MeV. All samples were irradiated at room temperature. In addition to STP, temperature changes can be observed when the particles are exposed to high energy for a long time. At STP, nanoscale Al particles combine with the oxygen of the air and form Al2O3. Also, X-ray diffraction study showed that the instability does not only belong to Al particles but also to Al2O3 in view of the fact that precarious Al(OH)3 crystal structures were observed. Thus, radiation dependence of lattice parameters was obtained, the mechanism of change of lattice parameters was determined due to radiation.

Interaction of ceria and erbia in air within temperature range 1500–600 °C

Phase equilibriums and structure transformations in the CeO2–Er2O3 system have been studied within 1500–600 °C in the full concentration range using XRD and petrography methods. It was established that the system is characterized by the formation of solid solutions on the basis of cubic modification of Er2O3 (C-type) and fluorite CeO2 (F-type). Solubility limits and concentration dependences of lattice parameters were determined for the phases forming in the system.

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.

Determination of temperature dependence of lattice parameters at three successive phase transitions m3m-4mm-mm2-3m

The temperature dependence of lattice parameters at three structural phase transition was determined from the condition of paraelectric phase macrosymmetry conservation in a polydomain crystal. Three analytical solutions for a second order phase transition are obtained. The analysis of the functions was made on the sample in BaTiO3. It is shown that one solution corresponds to the tetragonal and rhombohedral phases, the second one corresponds to orthorhombic phase, and the third solution is not realized.

Magnetic and transport behaviors of non-centrosymmetric Nd7Ni2Pd

Crystallographic, magnetic, electrical transport and thermodynamic properties of pseudo-binary Nd7Ni2Pd compound have been studied using temperature-dependent x-ray powder diffraction and physical property measurements. Compared to the ferromagnetic parent Nd7Pd3, the ground state of Nd7Ni2Pd is antiferromagnetic, and it exhibits strong metamagnetism. The measurements indicate two antiferromagnetic transitions in fields less than 8 kOe: a second-order paramagnetic to antiferromagnetic at TN2 = 29 K and a weak first-order antiferromagnetic to antiferromagnetic transition at TN1 = 24.5 K. The compound becomes ferromagnetic in fields of 8 kOe and higher with TC = 30 K. Temperature dependence of lattice parameters is anomalous, most prominently in the basal plane at ∼30 K; however, there is no detectable structural distortion or clear volume discontinuity around 25 K, suggesting a significant weakening of the first-order transition when compared to the binary Nd7Pd3.

Synthesis, growth and structural properties of (Cu<sub>1-x</sub>Ag<sub>x</sub>)<sub>7</sub>GeSe<sub>5</sub>I solid solutions

Проведено синтез та вирощування монокристалів твердих розчинів (Cu 1-x Ag x ) 7 GeSe 5 I. Рентгеноструктурні дослідження показали, що у системі Cu 7 GeSe 5 I – Ag 7 GeSe 5 I утворюється неперервний ряд твердих розчинів (Cu 1-x Ag x ) 7 GeSe 5 I, які кристалізуються в гранецен­трованiй кубiчнiй комiрцi . Встановлено, що концентраційна зміна параметра гратки відбувається у відповідності до закону Вегарда.