Refined Lattice Parameters Research Articles

Crystal and Local Structures of Pr2Co7Dx during Its Deuterium Absorption Process Determined by Neutron Diffraction.

We investigated crystal and local structures of Pr2Co7, Pr2Co7D2.7 and Pr2Co7D7.2 by neutron diffraction. The determined structural model of Pr2Co7D2.7 was the Ce2Ni7-type structure by Rietveld refinement, where the deuterium atoms occupied both the CaCu5-type (I) and the MgZn2-type cells. The deuterium contents in these cells were 0.10 and 0.80 D/M, respectively. The expansions of the lattice parameters of Pr2Co7D2.7 from the original intermetallics were Δa = 0.3% and Δc = 7.3%. The crystal structure transformed in the order Ce2Ni7-type Pr2Co7 → Ce2Ni7-type Pr2Co7D2.7 → orthorhombic Pr2Co7D7.2. The expansions of the lattice parameters of Pr2Co7D7.2 from the original intermetallics were Δa = 5.9%, Δb = 6.2%, and Δc = 6.4%; nearly isotropic expansion was observed. The deuterium contents in the MgZn2-type, CaCu5-type (I), and CaCu5-type (II) cells were 1.11, 0.44, and 0.83 D/M, respectively. The refined structural parameters by a pair distribution function (PDF) analysis on Pr2Co7 (0.18 < r < 5.0 nm) and Pr2Co7D2.7 (0.13 < r < 5.0 nm) obtained were consistent with those obtained by Rietveld refinement. The Rietveld refinement results of the refined lattice parameters of Pr2Co7D7.2 corresponded with the PDF analysis results in the region of 0.13 < r < 5.0 nm, whereas the refined atomic coordinates of the atoms D1, D2, D4, D6, and D9 obtained by the two methods differed. The refined structural parameters of the short-range structure (0.13 < r < 1.0 nm) in Pr2Co7D7.2 did not correspond to those of the long-range structure (0.13 < r < 5.0 nm). The local distortion within the domain of approximately 1.0 nm in size exists in Pr2Co7D7.2.

Comprehensive analysis of organic dye doped metal-coordinated single crystals: A study of structural, optical, thermal, dielectric, piezoelectric and mechanical characteristics

Comprehensive analysis of organic dye doped metal-coordinated single crystals: A study of structural, optical, thermal, dielectric, piezoelectric and mechanical characteristics

Computational and experimental investigations on structural, electronic and optical properties of scheelite compounds

Oxide of tungstate has consistently been pursued for use in optoelectronic applications. This study details the synthesis of AWO4 (A = Ba, Sr and Ca) using a high-temperature solid-state method. Additionally, theoretical calculations highlight its electronic structure, density of states, photoelectric properties, and vibrational modes. The x-ray diffraction of AWO4 (A = Ba, Sr and Ca) was meticulously introduced by the utilization of Rietveld for refinement. The refined lattice parameters substantially verified AWO4 (A = Ba, Sr and Ca) as a tetragonal system of scheelite with the spatial group of I41/a, and demonstrated significant alteration with the discrepancy in the radius of alkaline earth metal (A-site) ions. The electronic configuration and optical attributes of AWO4 (A = Ba, Sr and Ca) possessing scheelite-like structure were explored using density functional theory (DFT) based computational techniques. The theoretical blueprint was derived by optimizing the structure based on defects. The postulated optical bandgap energy confirms the occurrence of direct electronic transitions at Brillouin region G points. Calculations suggested the direct band gaps of BaWO4, SrWO4, and CaWO4 at 4.385, 3.123 and 3.813 eV. This was attributed to the energy levels produced by O and A-site atoms in the valence band, and W and O atoms in the conduction band. An examination of the polarization effect and uneven electronic charge distribution between [CaO8]6− and [WO4]2− clusters brought about by structural defects in AWO4 (A = Ba, Sr and Ca) was performed. Moreover, advanced investigations have been conducted on the elastic constants and mechanical durability of AWO4 (A = Ba, Sr and Ca). This research extensively calculated the elastic moduli of various matrices utilizing DFT. The critical Pugh’s ratio value was found to be >1.75, it indicated that AWO4 (A = Ba, Sr and Ca) has significant potential as a resilient material.

Co-precipitation process as an effective and viable route for proton-conducting solid oxide fuel cell applications

Co-precipitation process as an effective and viable route for proton-conducting solid oxide fuel cell applications

Isothermal section of the La2O3-Lu2O33-Er2O3 ternary phase diagram at 1250°С

The phase equilibria in the ternary La2О3–Lu2O3–Er2O3 system at 1250°C were studied by X-ray diffraction, and electron microscopy in the overall concentration range. At 1250°С in the La2О3–Lu2O3–Er2O3 system solution fields are formed based on cubic (C) modification of Lu2O3(Er2O3), hexagonal (A) modification of La2O3, as well as ordered phase structure perovskite-type LaLuO3 (LaErO3) (R). The isothermal section of the La2O3–Lu2O3–Er2O3 phase diagram at 1250°C has shown the three one-phase fields (A-La2O3, R, C-Lu2O3(Er2O3)) corresponding to solid solutions based on starting components and two dual-phase fields (C+R, A+R) between them. The refined lattice parameters of the unit cells for solid solutions and microstructures of the definite field of compositions for the systems solid were determined.

Superconductivity in a breathing kagome metals ROs2 (R = Sc, Y, Lu)

We have successfully synthesized three osmium-based hexagonal Laves compounds ROs2 (R = Sc, Y, Lu), and discussed their physical properties. LeBail refinement of pXRD data confirms that all compounds crystallize in the hexagonal centrosymmetric MgZn2-type structure (P63/mmc, No. 194). The refined lattice parameters are a = b = 5.1791(1) Å and c = 8.4841(2) Å for ScOs2, a = b = 5.2571(3) Å and c = 8.6613(2) Å for LuOs2 and a = b = 5.3067(6) Å and c = 8.7904(1) Å for YOs2. ROs2 Laves phases can be viewed as a stacking of kagome nets interleaved with triangular layers. Temperature-dependent magnetic susceptibility, resistivity and heat capacity measurements confirm bulk superconductivity at critical temperatures, Tc, of 5.36, 4.55, and 3.47 K for ScOs2, YOs2, and LuOs2, respectively. We have shown that all investigated Laves compounds are weakly-coupled type-II superconductors. DFT calculations revealed that the band structure of ROs2 is intricate due to multiple interacting d orbitals of Os and R. Nonetheless, the kagome-derived bands maintain their overall shape, and the Fermi level crosses a number of bands that originate from the kagome flat bands, broadened by interlayer interaction. As a result, ROs2 can be classified as (breathing) kagome metal superconductors.

Tracking Lattice Distortion Induced by Defects and Framework Tin in Beta Zeotypes.

The use of powder X-ray diffraction (PXRD) coupled with lattice parameter refinement is used to investigate the crystal structure of Sn-Beta materials. A newly developed semiempirical PXRD model with a reduced tetragonal unit cell is applied to obtain the characteristic crystallographic features. There is a robust correlation between lattice parameters and the concentration of tin and defects for materials prepared via hydrothermal (HT) and postsynthetic (PT) methods. With tin incorporation, PT Sn-Beta samples, which possess a more defective structure, exhibit an extended interlayer distance in the stacking sequence and expansion of the translation symmetry within the layers, leading to larger unit cell dimensions. In contrast, HT Sn-Beta samples, having fewer defects, show a minimal effect of tin site density on the unit cell volume, whereas lattice distortion is directly correlated to the framework tin density. Furthermore, density functional theory (DFT) studies support an identical trend of lattice distortion following the monoisomorphous substitution of T sites from silicon to tin. These findings highlight that PXRD can serve as a rapid and straightforward characterization method to evaluate both framework defects and heteroatom density, offering a novel approach to monitor structural changes and the possibility to evaluate the catalytic properties of heteroatom-incorporated zeotypes.

Crystal growth and phase formation of high‐entropy rare‐earth monoclinic aluminates

AbstractFor the first time, high‐entropy rare‐earth monoclinic aluminate crystals were grown via directional solidification using the micro‐pulling‐down method. Five high‐entropy compositions were formulated with a general formula RE4Al2O9, where RE is an equiatomic mixture of five rare‐earth elements. The rare‐earth elements included were Lu, Yb, Er, Y, Ho, Dy, Tb, Gd, Eu, Sm, Nd, and La. High‐temperature powder X‐ray diffraction and Rietveld structure refinement indicated that all crystals were a single monoclinic phase and that rare‐earth average ionic radius did not affect phase purity. At room temperature, the refined lattice parameters increased consistently with increasing average ionic radii of the five compositions. One of the crystals had a typical high‐temperature phase transition of single‐RE RE4Al2O9 in the range of 1100–1150°C, which consisted of a lattice contraction upon heating. Differential scanning calorimetry indicated a thermal event corresponding to that phase transition. Electron probe microanalysis revealed Al‐rich inclusions on the surface of the crystals. Crystals containing Tb had dark surface features that became lighter after annealing in a reducing atmosphere, which indicated that Tb4+ may be responsible for the dark features.

Exceptionally small Young modulus in 10M martensite of Ni-Mn-Ga exhibiting magnetic shape memory effect

Exceptionally small Young modulus in 10M martensite of Ni-Mn-Ga exhibiting magnetic shape memory effect

STUDY OF STRUCTURAL AND TRANSPORT PROPERTIES OF CuFe2O4 SYNTHESISED VIA LOW COST SOLID STATE REACTION ROUTE

ABSTRACT The ceramic compound CuFe2O4 was synthesised via conventional high-temperature solid-state reaction route. The structural study of the compound was done using X-ray diffraction technique. The preliminary structural study was performed using POWD software and a tetragonal structure was suggested. The Rietveld refinement of XRD (X-ray Diffraction) data was carried out using FullProf software and the refined lattice parameters were obtained as a = 5.80030 Å and c = 8.69400 Å with high tetragonality ratio. The crystallite size and lattice strain were calculated using Williamson–Hall (W-H) plot. The temperature and frequency dependent electrical properties of this compound are analysed using complex impedance technique. The impedance and modulus study of the compound showed the contribution of intra-grain effect to the overall electrical response. The studied ceramic possessed a non-Debye-type relaxation mechanism. The bulk resistance decreased with the increase in temperature, thus showing negative temperature coefficient of resistance behaviour. Modulus and conductivity study showed the evidence of conduction via hopping mechanism inside the material. Frequency-dependent AC conductivity followed Jonscher’s universal power law. The Arrhenius equation was fitted with the temperature-dependent AC conductivity at different frequencies, and activation energies were determined to understand the charge species involved in the conduction mechanism.

Structural analysis of Ba0.8Sr0.2Ti0.6Zr0.3Mn0.1O3 ceramics

Polycrystalline Ba0.8Sr0.2Ti0.6Zr0.3Mn0.1O3 was synthesized by solid-state reaction at 1600°C. The single phase formation of the compound without any impurities was confirmed by the X-ray diffraction technique. The prepared compound crystallized to a cubic structure with a space group of Pm-3m and the refined lattice parameters were a = b = c = 4.0253 Ǻ, α = β = γ = 90°. Rietveld refinement was carried for the powder XRD data using GSAS software and the experimental data peaks were indexed by Powder X software.

Comparison of the synthesis of s, p, d, and f block simple oxides of MgO, SnO2, NiO, and CeO2 nanostructured materials

The s, p, d, and f block simple oxides of MgO, SnO2, NiO, and CeO2 materials were synthesized by precipitation method and compared in this article. The tetragonal SnO2 and cubic CeO2 phases form in a single-step synthesis process. On the other hand, upon annealing (500 °C/3h), the as-prepared trigonal (P-3 m1 (1 6 4)) Mg(OH)2 and Ni(OH)2 phase materials transform into cubic (Fm-3 m (2 2 5)) oxides of MgO and NiO. The difference in the ionic radii of these ions (Mg2+, Sn4+, Ni2+, and Ce4+) is significantly reflected in the variation in the refined lattice parameters. The nanostructured as-prepared materials (SnO2 and CeO2) obtained in a single-step process show the crystalline size (average) of 2 nm. Conversely, the samples of MgO and NiO phases obtained through annealing show 13.76 nm and 21.44 nm, respectively. The as-prepared materials show the weight loss of 33.3%, 31.7%, 15.4%, and 16.1% at the end temperature (1000 °C) for the Mg(OH)2, Ni(OH)2, SnO2, and CeO2 phases, respectively. The different FTIR bands are seen between the wavenumber 4000 and 400 cm−1 for the present series samples..

Molecular‐level composition design for efficient synthesis of SiAlON ceramics

AbstractSiAlONs are a class of liquid‐phase sintered ceramics with excellent room‐temperature strength and toughness, but whose residual grain boundary glass softens at high temperatures, limiting use in extreme environments. For this reason, efforts are made to minimize the volume of the grain boundary glass while still facilitating full densification. This work describes a potential route for the densification of SiAlONs with very low concentrations of liquid‐phase sintering additive (e.g., rare‐earth oxides such as yttria) by using an organometallic precursor. Solid solution of Al and O in the Si3N4 lattice was accomplished through the incorporation of solute atoms via liquid organic precursor aluminum sec‐butoxide (ASB). Al2O3 powder is conventionally used for this purpose, and the subsequent lattice softening associated with the solid solution helps to facilitate densification. However, a liquid‐phase additive is still essential for the full densification of SiAlONs. Higher densities were obtained from SiAlON powder blends utilizing organometallic ASB than those utilizing alumina powder, allowing for greater densification at very low Y2O3 concentrations. The thermal decomposition of the organic precursor was investigated by high‐temperature scanning electron microscopy, thermogravimetric analysis, and various X‐ray diffraction experiments. Immersion density measurements and lattice parameter refinements were performed for samples sintered with varying Y2O3 concentrations and/or dwell times. Results indicate that ASB‐containing powder blends favor SiAlON formation more strongly than Al2O3‐containing powder blends and favor densification at very low Y2O3 concentration.

Experimental investigation of the phase equilibria, phase stability, and defect structure in the Cr–Zr system by using DSC, XRD, and SEM

The solid-state phase transformations, phase stability, and defect structure in the Cr–Zr system were investigated experimentally by using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Scanning electron microscope (SEM) along with EDX. Arc melting was used to synthesize all of these alloys. The temperature of the Cr and Zr-rich eutectic L ↔ C36–Cr2Zr + Cr and L ↔ β-Zr + C15–Cr2Zr were determined to be 1861 ± 3 K and 1588 ± 3 K, respectively. The temperature corresponding to the eutectoid transformation β-Zr ↔ α-Zr + C15–Cr2Zr was found to be 1099 ± 2 K. The temperature pertaining to C36–Cr2Zr ↔Cr + C15–Cr2Zr transformation were determined to be 1844 ± 3 K. These values are notably different from previous measurements and are more accurate. The liquidus temperature in the composition range from 60 to 100 at.% Zr was measured for the first time. All the alloy specimens were characterized by X-ray diffraction. The lattice parameters and relative phase fraction of the constituent phases were evaluated by using Rietveld refinement of the XRD data. At ambient temperature, the refined lattice parameter of C15–Cr2Zr increases linearly with Zr concentration from 31 (7.199 Å) to 34 at.% Zr (7.210 Å). The oxygen impurities play an important role in the sluggish transformation of the C14/C36–Cr2Zr ↔ C15–Cr2Zr Laves phase. The density calculated based on lattice parameters determined by XRD and the theoretical model for anti-site type defects makes it is fair to conclude that C15–Cr2Zr Laves phase is a substitutional type solid solution. The experimental data presented here is consistent and reliable, and it supersedes previous findings.

Ambiguous structure determination from powder data: four different structural models of 4,11-di-fluoro-quinacridone with similar X-ray powder patterns, fit to the PDF, SSNMR and DFT-D.

Four different structural models, which all fit the same X-ray powder pattern, were obtained in the structure determination of 4,11-di-fluoro-quinacridone (C20H10N2O2F2) from unindexed X-ray powder data by a global fit. The models differ in their lattice parameters, space groups, Z, Z', molecular packing and hydrogen bond patterns. The molecules form a criss-cross pattern in models A and B, a layer structure built from chains in model C and a criss-cross arrangement of dimers in model D. Nevertheless, all models give a good Rietveld fit to the experimental powder pattern with acceptable R-values. All molecular geometries are reliable, except for model D, which is slightly distorted. All structures are crystallochemically plausible, concerning density, hydrogen bonds, intermolecular distances etc. All models passed the checkCIF test without major problems; only in model A a missed symmetry was detected. All structures could have probably been published, although 3 of the 4 structures were wrong. The investigation, which of the four structures is actually the correct one, was challenging. Six methods were used: (1) Rietveld refinements, (2) fit of the crystal structures to the pair distribution function (PDF) including the refinement of lattice parameters and atomic coordinates, (3) evaluation of the colour, (4) lattice-energy minimizations with force fields, (5) lattice-energy minimizations by two dispersion-corrected density functional theory methods, and (6) multinuclear CPMAS solid-state NMR spectroscopy (1H, 13C, 19F) including the comparison of calculated and experimental chemical shifts. All in all, model B (perhaps with some disorder) can probably be considered to be the correct one. This work shows that a structure determination from limited-quality powder data may result in totally different structural models, which all may be correct or wrong, even if they are chemically sensible and give a good Rietveld refinement. Additionally, the work is an excellent example that the refinement of an organic crystal structure can be successfully performed by a fit to the PDF, and the combination of computed and experimental solid-state NMR chemical shifts can provide further information for the selection of the most reliable structure among several possibilities.

The crystal chemistry and electrical properties of Fe doped Ca12Al14O33 (Mayenite)

&#x0D; &#x0D; &#x0D; X-ray and neutron powder diffraction have been used to study the crystal chemistry of Fe doped mayenite (Ca12Al14-xFexO33). Solid- state synthesis was used to prepare Ca12Al14-xFexO33 where x = 0, 0.1, 0.2, 0.5 and 0.6 and the citrate gel route was used to prepare Ca12Al14-xFexO33 where x = 0, 0.05, 0.1, 0.2, 0.3 and 0.4. X-ray powder diffraction data indicate that samples with the same composition but synthesized by the citrate gel route were more likely to be phase pure than samples obtained by traditional solid-state synthesis. The refined lattice parameters were observed to increase with increasing Fe concentration, irrespective of the synthesis method. Refined neutron powder data confirm that Fe is going into Al site rather than Ca site. A 2-point probe was used to measure the electrical properties of the Fe doped citrate gel synthesized samples and showed that the resistivity increases for the Fe doped samples compared to the undoped mayenite.&#x0D; &#x0D; &#x0D;

New layered quaternary BaCu6Sn2As4−x and BaCu6Sn2P4−x phases: Crystal growth and physical properties

We report two new quaternary BaCu6Sn2As4−x and BaCu6Sn2P4−x phases with a new structure type, which are fully characterized by single crystal X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). These two phases crystallize in tetragonal cell with space group I4/mmm (#139) and Pearson symbol tI26. The refined lattice parameters are a = 4.164(1) Å, c = 24.088(3) Å for BaCu6Sn2As4−x, and a = 4.053(2) Å, c = 24.08(1) Å for BaCu6Sn2P4−x, respectively. They possess a distinct layered feature composed of Cu6Sn2Pnx (Pn = P, As) layers sandwiched by the Ba atoms. The Cu-Sn framework of the Cu6Sn2Pnx layer is closely related to the well-known Cu2Sb-type structure, and Pn atoms are found occupying two interstitial sites caused by close packing of Cu and Sn atoms or capped on the top of square nets formed by Cu atoms. The compounds are also characterized by electrical transport measurements down to 2 K.

Novel pyrochlore-structured bismuth iron antimonates: Structural, impedance and electrochemical studies

• BFS pyrochlores were prepared by solid-state reaction. • A one-to-one chemical substitution of Sb 5+ by Fe 3+ together with oxygen non-stoichiometry was proposed. • The thermally stable BFS pyrochlores exhibited moderate high ε' and low tan δ . • The BFS thin films revealed good capacitive behaviour and electrochemical reversibility. A moderate pyrochlore solid solution range of 0.00 ≤ x ≤ 0.64 was observed in the Bi 3.36 Fe 2.08+x Sb 2.56-x O 14.56-x (BFS) system prepared by solid-state reaction at 925 °C for 2 days. The overall charge compensation required a one-to-one cationic replacement and oxygen vacancies, i.e. Sb 5+ ↔Fe 3+ - O 2– . BFS cubic pyrochlores showed their refined lattice parameters varying linearly in the range of 10.4284 (8)-10.4513(8), thus obeying the Vegard's rule. The measured crystallite sizes by both Scherrer and Williamson-Hall methods were found to be in the range of 46–67 nm; whilst, the larger grain sizes in the range of 0.2–2.9 μm were calculated using scanning electron microscopy (SEM) analysis. The AC impedance analysis also verified a few electrical responses of BFS pyrochlores: (i) BFS pyrochlores had moderate dielectric constants in the range of 24–35 and dielectric losses in the order of 10 −1 at room temperature and 1 MHz, (ii) BFS pyrochlores were not electrically homogeneous with bulk capacitances in the order of 10 −12 Fcm −1 , (iii) a non-Debye type and temperature-dependent relaxation process were discernible and (iv) the movement of charge carrier were either in the long-range or short-range migration subjected to time availability. In addition, BFS pyrochlore thin films had a good capacitive behaviour and electrochemical reversibility, according to the cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) analyses. All these excellent properties rendered BFS pyrochlores to be a suitable material for Class 1 ceramic capacitors.

Phase equilibria in the La2O3-Y2O3-Nd2O3 system at 1500 °C

The phase equilibria in the ternary La 2 O 3 -Y 2 O 3 -Nd 2 O 3 system at 1500 °C were studied by X-ray diffraction, petrography, and electron microscopy in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcination at 1100 and 1500 °C. The solid solutions based on various polymorphous forms of source components and ordered phase of LaYO 3 were revealed in the system. The isothermal section of the phase diagram for the La 2 O 3 -Y 2 O 3 -Nd 2 O 3 system has been developed. It was established that in the ternary La 2 O 3 -Y 2 O 3 -Nd 2 O 3 system there exist fields of solid solutions based on hexagonal (A) and monoclinic (B) modifications of La 2 O 3 and Nd 2 O 3 , cubic (C) modification of Y 2 O 3 , as well as perovskite-type structure of LaYO 3 (R) with rhombic distortions. The systematic study that covered the whole composition range excluded the formation of new phases. The refined lattice parameter of the unit cell and the boundaries of the homogeneity fields for solid solutions were determined.

Enhanced High-Rate Performance of Nanosized Single Crystal ε-VOPO4 with Niobium Substitution for Lithium-Ion Batteries

ε-VOPO4 has the potential to be the next high energy density cathode material for lithium-ion batteries due to its high thermal stability and its ability to reversibly intercalate two full Li+, giving a high discharge capacity of 305 mAh g−1. However, vanadyl phosphate materials typically experience poor Li+ kinetics that impedes the high-rate capability at the high voltage plateau. In this work, we applied niobium substitution to improve the high-rate performance of the 4.0 V plateau of ε-VOPO4. Elemental analysis and lattice parameter refinements determined that up to 10% Nb can be substituted into ε-VOPO4 without any impurities. TEM and Synchrotron-based EXAFS confirmed that all the substituted samples have Nb in the ε-VOPO4 structure. Electrochemical tests revealed that 1% Nb substitution can deliver a high discharge capacity of ∼300 mAh g−1 without any degradation in cycling behavior by maintaining its nanosized morphology.