Variation Of Unit Cell Volume Research Articles

Hydrostatic pressure response of semiconducting GaSb applying a semi-empirical approach

In addition to experimental investigations, semi-empirical approaches prove valuable for replicating experimental results and predicting material behavior under high-pressure conditions. This study investigates the variation of unit cell volume in cubic zinc blende Gallium antimonide (GaSb) up to the phase transition pressure, relying solely on structural parameters from literature measurements at ambient conditions. The research extends to inspect the impact of high pressure on various properties, including mass density, bulk modulus, bulk sound wave velocity, microhardness, first-order pressure derivative of the isothermal bulk modulus, Grüneisen parameter, and Debye temperature for the GaSb compound. The bulk modulus and microhardness show nearly linear increases with pressure, while sound wave velocity and Debye temperature exhibit nonlinear variations. The first-order pressure derivative of the bulk modulus and Grüneisen parameter gradually decreased in the material under study. Similar trends under pressure are found in literature for materials with different crystallographic structures. Additionally, the study predicts and analyzes extra physical parameters of GaSb, comparing them with existing literature data.

Understanding of structural evolution, dielectric performance, and photoluminescence behavior of Sm-modified Na0.5Bi0.5TiO3

We present the crystal structures, dielectric and optical performance of Samarium doped NBT ceramic, (Bi(1−x)Smx)0.5Na0.5TiO3for x = 0.0, 0.01, 0.02, 0.03, 0.04, 0.05 fabricated by a solid-state reaction method. The Rietveld refinement outcomes of XRD data show that all the samples have rhombohedral crystal structures with the R3c space group. The variation of unit cell volume with composition displays an anomaly at x = 0.03. The Raman modes centered at 258 cm−1 and 535 cm−1 become broader with trivial smearing towards higher wavelength through a rise in Sm percentage. The temperature corresponding to maximum permittivity attains maximum value at x = 0.03. We found that dielectric loss decreases with increasing Sm content. The diffusing nature of the phase transition is enhanced with the rise in dopant concentration of Sm. The bandgap energy obtained from the reflectance data of UV–visible spectroscopy increases x = 0.03 and afterward simultaneously diminishes with Sm concentration. The photoluminescence study was carried out using the excitation spectra and emission spectra. The most intense emission has been observed at x = 0.03. Besides, a feeble green emission peak at 564 nm and two burly red emission peaks at 600 nm and 646 nm correspond to the 4G5/2→6H5/2 transition, and 4G5/2→6H7/2 and 4G5/2→6H9/2 transitions respectively. We expect that the incorporation of Sm in the NBT system will be a suitable method to highlight the multifunctional characteristics of the material for potential applications in devices having manifold functions incorporated with electrical and luminescence properties.

Exploration of crystal structure, and luminescence behaviors of Terbium-activated CaWO4 phosphor

This manuscript includes structural, optical, photoluminescence, and thermoluminescence behaviors of Terbium incorporated CaWO4 samples with nominal compositions of Ca1-xTb2x/3WO4 (x = 0.01, 0.02, 0.03, 0.04, 0.05) prepared by the traditional solid-state reaction route. Results found from the Rietveld refinements of X-ray diffraction patterns confirmed that all the samples have tetragonal crystal structures with I41/a space group. The variation of unit cell volume with the compositions shows an anomaly at x = 0.03. Band gap energy values of these synthesized samples are found from the UV–Visible absorbance spectra with increasing order. Photoluminescence behaviors, as well as the FWHM values, are analyzed from the excitation along with the emission spectra. Critical quenching concentration at x = 0.03 with a critical energy transfer distance of ∼ 20 Å caused by the dipole-dipole interactions is found in these spectra. CIE Chromaticity coordinates are indicated the green emission color of all the prepared samples with high color purity, correlated color temperature, color rendering index, and luminous efficiency of radiation values. Quantum efficiency of the material with x = 0.03 Tb concentration is observed under 255 nm excitation wavelength. PL decay analyses of the phosphors are carried out and the average lifetime values are calculated. Thermoluminescence spectroscopy of x = 0.03 irradiating by 15 min of UV dose is described as the lower UV dosimetry and second-order kinetics of the material.

Interfacial Space Charge Enhanced Sodium Storage in a Zero‐Strain Cerium Niobite Perovskite Anode

AbstractIntercalation electrode materials store Na by incorporation into their framework structure without phase transformation and substantial large volume, resulting in the excellent cycling stability during electrochemical cycling. However, challenges arise due to a low capacity of intercalation electrode for sodium‐ion batteries (SIBs). Here, a perovskite oxide (Ce1/3NbO3 (CNO)) as an intercalation anode with dual functions of high capacity and excellent cycling stability is explored. The Na+ storage capacity of CNO (141.3 mAh g‐1) originates from not only sufficient cation vacancies but also the interfacial space charge storage of Na+ in the surface of CNO particles. Additionally, CNO exhibits excellent cycling stability with 90.2% capacity retention after 1000 cycles at 1 C, 99.4% capacity retention after 2000 cycles at 5 C, and 96.5% capacity retention after 10 000 cycles at 10 C. The cycling performance can be explained by the “zero‐stain” Na+ storage characteristic, where the maximal unit cell volume variation induced by Na+ insertion/extraction is calculated to be only 0.38%. Hence, CNO is a promising alternative for long‐life SIBs. The mechanisms that enable the storage of Na+ with negligible volume variation will guide new insights for the rational design of ultra‐stable electrode materials for SIBs.

Coupling between elastic strains and phase transition in dense pure zirconia polycrystals

A deep understanding of the solid-state phase transition processes of zirconia is a mandatory requirement for the development of new zirconia-based materials useful for many industrial applications. For five decades, the monoclinic $\ensuremath{\Leftrightarrow}$ tetragonal phase transition is described as a martensitic one and it is well known that it is associated with a large unit cell volume variation that promotes the appearance of elastic strains and also microcracking. In the present paper, we study, through in situ high temperature x-ray diffraction experiments, the coupling between strain relaxation and the martensitic phase transition into a pure zirconia bulk polycrystal. Quantitative analysis of the diffraction signal allows us to disentangle, with respect to the temperature variation, the phase transition and the microcracking processes, and we demonstrate that a high temperature postelaboration thermal treatment induces an increase in the stored elastic energy. Finally, we show that in such polycrystals exhibiting a crystal size distribution and in which the crystals are under internal stresses, the tetragonal to monoclinic phase transition process evolves from a first order one to a second order one when the temperature decreases.

Azetidinium Lead Halide Ruddlesden-Popper Phases.

A family of Ruddlesden–Popper (n = 1) layered perovskite-related phases, Az2PbClxBr4−x with composition 0 ≤ x ≤ 4 were obtained using mechanosynthesis. These compounds are isostructural with K2NiF4 and therefore adopt the idealised n = 1 Ruddlesden–Popper structure. A linear variation in unit cell volume as a function of anion average radius is observed. A tunable bandgap is achieved, ranging from 2.81 to 3.43 eV, and the bandgap varies in a second-order polynomial relationship with the halide composition.

Progressive Polytypism and Bandgap Tuning in Azetidinium Lead Halide Perovskites.

Mixed halide azetidinium lead perovskites AzPbBr3-xXx (X = Cl or I) were obtained by mechanosynthesis. With varying halide composition from Cl- to Br- to I-, the chloride and bromide analogues both form in the hexagonal 6H polytype while the iodide adopts the 9R polytype. An intermediate 4H polytype is observed for mixed Br/I compositions. Overall, the structure progresses from 6H to 4H to 9R perovskite polytype with varying halide composition. Rietveld refinement of the powder X-ray diffraction patterns revealed a linear variation in unit cell volume as a function of the average radius of the anion, which not only is observed within the solid solution of each polytype (according to Vegard's law) but also extends uniformly across all three polytypes. This is correlated to a progressive (linear) tuning of the bandgap from 3.43 to 2.00 eV. Regardless of halide, the family of azetidinium halide perovskite polytypes are highly stable, with no discernible change in properties over more than 6 months under ambient conditions.

Pressure-induced octahedral tilting distortion and structural phase transition in columbite structured NiNb2O6

High-pressure behavior of the technologically important compound NiNb2O6 adopting a columbite-type orthorhombic structure at ambient pressure and temperature conditions was investigated using synchrotron x-ray powder diffraction, Raman spectroscopic measurements, and first-principles calculations. The x-ray diffraction data indicate the occurrence of irreversible pressure-induced structural phase transition in the studied compound beyond 9 GPa. The high-pressure phase is found to be monoclinic with space group P2/m. The large volume collapse (∼4.4%) at the transition indicates the nature of the transition to be of the first order. There is a change in oxygen anion coordination number around Nb from 6 to 8; however, the coordination number around Ni remains 6. The experimental pressure–volume data when fitted to the Birch−Murnaghan equation of states yield the value of ambient pressure bulk modulus (B0) as 178.7 (17) GPa for the orthorhombic phase and 244 (6) for the high-pressure monoclinic phase. The changes in Raman spectra indicate the distortion of NbO6 octahedra resulting in structural phase transitions. The logarithmic variation of unit cell volume (V) with optical lattice mode frequency (ν) helped us to calculate their respective Grüneisen parameters (γ) and it also supports the instability of the orthorhombic columbite structure of NiNb2O6 beyond 9 GPa, originated due to strong octahedral deformation of NbO6 octahedra. The variation of structural, electronic, and optical properties with pressure has also been discussed through first-principles calculations based on density functional theory using the revised Perdew–Burke–Ernzerh of generalized gradient approximation. The theoretical bandgap collapses and the distortion of NbO6 octahedra through the O chains with pressure are emphasized from the density of states data.

Effect of Vanadium Content on the Microwave Dielectric Properties of Sr2VxO7 (1.80 ≤ x ≤ 2.05) Ceramics

Vanadium content has a prominent effect on the microwave dielectric properties of Sr2VxO7 (1.80 ≤ x ≤ 2.05) ceramics, which is related to extrinsic factors and intrinsic factors, such as secondary phase, bulk density, crystal structure, and V–O bond length. Rietveld refinement, energy dispersive spectroscopy, and Raman spectra analysis revealed that an appropriate vanadium deficiency causes the appearance of secondary phase Sr3V2O8, which results in the variation of unit cell volume and the significant improvement of Q × f value and the temperature coefficient of resonant frequency. Specifically, the Sr2V1.90O7 ceramic sintered at 950°C possesses optimum microwave dielectric performances: the dielectric constant of 11.1, the Q × f value of 36,500 GHz, and the temperature coefficient of resonant frequency of − 35.6 ppm/°C.

A study of cluster spin-glass behaviour at the critical composition [formula omitted]NiGe

The solid solution Mn1-xFexNiGe with x~0.27 has been investigated via powder ray diffraction, dc magnetization, ac susceptibility, heat capacity, and magnetic relaxation measurements. The alloy Mn0.73Fe0.27NiGe crystallizes in a Ni2In-type hexagonal structure at room temperature. A coexistence of hexagonal and orthorhombic phases with a phase fraction of nearly 88:12 was found below 80 K. The dc susceptibility measurements reveal a paramagnetic to ferromagnetic transition at around Tt≃80 K and a thermal hysteresis observed during field-cooled-cooling and field-cooled-warming suggests the first order nature of the magnetic transition. The splitting between zero-field-cooled and field-cooled dc susceptibilities and the appearance of a frequency dependent peak in ac susceptibility indicate the onset of a spin-glass transition at Tg≃58 K. The relative shift in freezing temperature (δTf) is calculated to be ~0.03 and ~0.09, respectively from the real and imaginary parts of ac susceptibility indicating the formation of cluster spin-glass state. The analysis of frequency dependent Tf using power law yields a characteristic time for a single spin flip τ*≃1.5×10-10 s and critical exponent zν′≃5.5. Similarly, the analysis using the Vogel-Fulcher law results a characteristic time for a single spin flip τ0≃1.2×10-8 s, Vogel-Fulcher temperature T0≃54.8 K, and an activation energy Ea/kB≃72.8 K. The magnitude of τ* and τ0 together with a non-zero value of T0 add further evidence for the formation of cluster spin-glass. The magnetic relaxation and memory effect measurements also demonstrate the low temperature cluster spin-glass behaviour. The reason for the cluster spin-glass behaviour could be the difference in local environment of Mn atoms in the coexisting Mn-rich antiferromagnetic and Fe-rich ferromagnetic phases. Furthermore, Mn0.73Fe0.27NiGe shows the asymmetric response of magnetic relaxation with a change in temperature, belowTf, which can be explained by the hierarchical model. The low temperature heat capacity gives a large electronic coefficient γ≃25 mJ/mol K2 and the Debye temperature θD≃300 K. This value of θD is in close agreement with that calculated from the temperature variation of unit cell volume.

Crystal structure and enhanced microwave dielectric properties of Ta5+ substituted Li3Mg2NbO6 ceramics

AbstractComposition and structure play dominant roles in realizing the microwave dielectric properties that are necessary for the ever‐increasing demands of the Internet of Things and related communication technologies. In the present study, the substitution of Ta5+ in Li3Mg2Nb1−xTaxO6 ceramics and its effect on the structural characteristics and microwave dielectric performances is systematically studied. All the substituted compositions were determined to be pure phase orthorhombic Li3Mg2NbO6 structure of space group Fddd. Furthermore, a NbO6 octahedral distortion, Nb‐O bond valence, packing fraction and polarizability were calculated to explore the structure‐property‐performance paradigm in the context of microwave dielectric performance. Scanning electron microscopy revealed homogeneous microstructures, with the introduction of Ta5+ promoting grain growth. Raman spectra indicated that the variation of the band (blue shift and red shift) at 771 cm−1 was highly correlated with the variation in unit cell volume. The polarizability significantly impacted ɛr values. The Q × f values were strongly influenced by the packing fraction and grain size. The changes in the NbO6 octahedral distortion and Nb–O bond valence impacted the τf values. The Li3Mg2Nb0.98Ta0.02O6 composition displayed the most dramatic improvements in microwave dielectric properties: εr = 15.58, Q × f = 113 000 GHz and τf = −4.5 ppm/°C, providing a potential candidate for next generation microwave and millimeter‐wave applications.

Growth of α-Cr2O3 single crystals by mist CVD using ammonium dichromate

Ammonium dichromate and chromium chloride were examined via thermogravimetric and differential thermal analyses and used to grow α-Cr2O3 via mist chemical vapor deposition. Only the former resulted in noticeable film formation. Using ammonium dichromate, α-Cr2O3 single crystals were grown in a wide growth-temperature range of 300–440 °C. The dependences of the lattice constants a and c on the growth temperature and precursor concentration were explained by combination of (i) lattice reconstruction and (ii) unit-cell volume variation. A maximum growth rate of 10 nm/min; a low (0006) rocking-curve full width at half maximum of 150 arcsec; and low a and c lattice mismatches (with α-Ga2O3) of 0.7 and 1.4%, respectively, were achieved.

A comparative study of Sr-doped LaMnO3 synthesised via solid-state reaction and sol–gel methods

ABSTRACTThis work deals with the synthesis of hole-doped La1-xSrxMnO3 (x = 0.25 and 0.33) perovskite via two different ways, namely a solid-state reaction method and a sol–gel process. Various properties of the samples have been investigated and compared by means of different techniques, namely X-ray diffraction (XRD), temperature-dependent resistivity measurements in the temperature range 25–300 K using a closed cycle refrigerator and vibrating sample magnetometry (VSM). All samples have orthorhombic crystal symmetry and an irregular variation in unit-cell volume with increase in Sr content. The average crystallite size was determined from the XRD data and found to lie in the range 19–22 nm. Metal–insulator transitions (MIT) were observed in all the samples via low-temperature electrical characterisations. The magnetic measurements confirm that the magnetisation does not saturate for the 25% Sr doped samples up to the available field of 10 kOe. The magnetic response also supports the interpretation of XRD and resistivity data. The obtained results are explained on the basis of double-exchange and super-exchange mechanisms.

Thermal expansion of deuterated monoclinic natrojarosite; a combined neutron–synchrotron powder diffraction study

A combination of time-of-flight neutron diffraction and synchrotron X-ray powder diffraction has been used to investigate the thermal expansion of a synthetic deuterated natrojarosite from 80 to 440 K under ambient-pressure conditions. The variation in unit-cell volume for monoclinic jarosite over this temperature range can be well represented by an Einstein expression of the form V = 515.308 (5) + 8.5 (4)/{exp[319 (4)/T] − 1}. Analysis of the behaviour of the polyhedra and hydrogen-bond network suggests that the strength of the hydrogen bonds connected to the sulfate tetrahedra is instrumental in determining the expansion of the structure, which manifests primarily in the c-axis direction.

Colossal negative thermal expansion in reduced layered ruthenate

Large negative thermal expansion (NTE) has been discovered during the last decade in materials of various kinds, particularly materials associated with a magnetic, ferroelectric or charge-transfer phase transition. Such NTE materials have attracted considerable attention for use as thermal-expansion compensators. Here, we report the discovery of giant NTE for reduced layered ruthenate. The total volume change related to NTE reaches 6.7% in dilatometry, a value twice as large as the largest volume change reported to date. We observed a giant negative coefficient of linear thermal expansion α=−115 × 10−6 K−1 over 200 K interval below 345 K. This dilatometric NTE is too large to be attributable to the crystallographic unit-cell volume variation with temperature. The highly anisotropic thermal expansion of the crystal grains might underlie giant bulk NTE via microstructural effects consuming open spaces in the sintered body on heating.

Electron–phonon interaction in three-, two- and one-dimensional ternary mixed crystals

The electron–phonon (e–p) interaction in three-dimensional (3D), two-dimensional (2D) and one-dimensional (1D) ternary mixed crystals is studied. The e–p interaction Hamiltonians including the unit cell volume variation in ternary mixed crystals are obtained by using the modified random-element-isodisplacement model and Born–Huang method. The polaronic self-trapping energy and renormalized effective mass of GaAs[Formula: see text]Sb[Formula: see text], GaP[Formula: see text]As[Formula: see text] and GaP[Formula: see text]Sb[Formula: see text] compounds are numerically calculated. It is confirmed theoretically that the nonlinear variation of the self-trapping energy and effective mass with the composition is essential and the unit cell volume effects cannot be neglected except the weak e–p coupling. The dimensional effect cannot also be ignored.

Suppressing the Phase Transition of the Layered Ni-Rich Oxide Cathode during High-Voltage Cycling by Introducing Low-Content Li2MnO3.

The layered Ni-rich oxide cathode (LiNi0.8Co0.1Mn0.1O2) suffers from a tremendous structural degradation during high-voltage cycling (4.8 V), causing the drastic rise of electrode impedance and deterioration of the capacity retention. Here, we develop an effective strategy to overcome these problems of the Ni-rich cathode material through doping low-content Li2MnO3 as an excellent structure stabilizer. Cyclic voltammogram and ex-situ X-ray diffraction measurements have reveled that Li2MnO3 could display a remarkable suppression effect on the phase transition of LiNi0.8Co0.1Mn0.1O2. The electrochemical tests showed that Li2MnO3-stabilized LiNi0.8Co0.1Mn0.1O2 could realize the large reversible capacity, stable discharge voltage and excellent cycling life during high-voltage cycling, which could be benefited from the enhanced structural stability of the modified Ni-rich cathode. The Li2MnO3 could sufficiently suppress the phase transition between two hexagonal phase (H2 and H3) with distinctly different lattice parameters, significantly reducing variation of unit-cell volume, which facilitates stabilization of the original layered structure of LiNi0.8Co0.1Mn0.1O2 cathode during high-voltage cycling.

Electron–phonon interaction in quasi-1D ternary mixed crystals of polar semiconductors

The electron–optical-phonon interaction between an electron and two branches of LO-phonon modes in a quasi-one-dimensional ternary mixed crystal (TMC) of polar semiconductors is studied. The new electron–phonon interaction Hamiltonian including the unit-cell volume variation in TMCs is obtained by using the modified random element isodisplacement model and Born–Huang method. The energies of polaron are numerically calculated for several systems of III–V compounds. A group of III-nitride mixed crystals is also taken into numerical calculation in our theory. It is verified theoretically that the obvious nonlinearity of the polaronic energy and effective mass with the composition is essential and the unit-cell volume effects cannot be neglected except the very weak e–p coupling.

High-pressure X-ray Diffraction Study of SrSi2O2N2:Eu2+

SrSi2O2N2oxynitride crystallizes in the P1 space group [1]. This compound is an excellent host for phosphors, due to its superior thermal and chemical stability and large energy bandgap. Eu-doped SrSi2O2N2can be used in green LEDs, and as a green component in phosphor mixtures; it is suitable, in particular, for white LEDs. For application in LEDs, the most important feature of SrSi2O2N2:Eu2+is the intense broadband luminescence at about 530 nm. In this study, high-pressure X-ray powder diffraction (XRD) experiments are used in order to experimentally determine, for the first time, the equation of state (EOS) of SrSi2O2N2:Eu2+. The studied sample, with Eu content of 2% was prepared by solid state reaction. The in situ XRD experiment was performed at the I711 beamline of MAXII synchrotron (Lund, Sweden) for a sample mounted in a diamond anvil cell, using hydrostatic compression conditions. The applied X-ray wavelength was 0.9917 Å. In the pressure range studied (up to 9.6 GPa) the triclinic structure is found to be conserved. Lattice parameters a, b and c decrease smoothly but slightly anisotropically as a function of applied pressure, whereas the angles α, β and γ vary marginally. The material is the most compressible in the b direction and the least compressible in the a direction. Angles α and γ are almost constant whereas the value of β angle slightly increases with rising pressure. The variation of unit cell volume with pressure served for determination of the Birch-Murnaghan EOS: the resulting bulk modulus value is 103(5) GPa. The present bulk modulus value is by 22% smaller than those reported for other oxonitridosilicates such as SrSiAl2O3N2and Ce4[Si4O4N6]O (131.9(1) GPa and 131(2) GPa, respectively) [2].

Influence of silver doping on the magnetoresistance and temperature coefficient of resistance in Pr0.67Sr0.33MnO3

We have synthesized and investigated the effect of Ag doping in Pr0.67Sr1−xAgxMnO3 (0≤x≤0.3) perovskite materials via solid state reaction route. The structural, transport and magnetoresistance behavior have been studied. The Rietveld refinement of X-ray diffraction data shows that the compounds crystallize in an orthorhombic structure with Pnma space group with systematic non-linear variation in unit cell volume and lattice parameters. The grain morphology confirms that silver enhances conducting channels and reacts well with the compound only upto a certain doping level. The temperature dependent zero-field and in-field resistivity have been measured between 5K and 300K. The samples exhibit a systematic variation in metal to insulator transition temperature and a large magnetoresistance at x=0.10. The highest value of temperature coefficient of resistance has been observed by us for the first time. The results revealed that Ag takes part in the reaction only when the doping amount is small and at higher doping the system becomes a two phase composite.