Lattice Constant Decreases Research Articles

The structure and electrical properties of novel BaSn0.15Ce0.35Hf0.25Y0.1Yb0.1Ho0.05O3-δ high-entropy proton-conducting electrolyte

In this article, the structure and electrical properties of BaSn0.15Ce0.35Hf0.25Y0.1Yb0.1Ho0.05O3-δ (referred as BSCHYYbHo in forthcoming discuss) high-entropy ceramic have been investigated. The BCHYYb (short for BaCe0.5Hf0.3Y0.1Yb0.1O3-δ) and BSCHYYbHo pellets were synthesized successfully by the solid-state reaction method. The XRD detection results indicate that there is no secondary phase appeared in BSCHYYbHo and the lattice constant decrease compared to BCHYYb. The surface SEM and EDS images illustrates that BSCHYYbHo is denser than BCHYYb and the elements distribution is more uniform. The DFT calculation proves that BSCHYYbHo has a tend to maintain single phase structure. The electrical properties of BSCHYYbHo is obtained by the DRT analysis and equivalent circuit method based on defect equilibria model. The total conductivity of BSCHYYbHo is about 2.02 × 10-4 ∼1.01 × 10-2 S·cm-1 and standard molar hydration enthalpy of BSCHYYbHo is recorded as − 81.8 kJ/mol. Further, the proton, oxygen vacancies and electron holes conductivity activation energies in BSCHYYbHo is estimated to be 0.45 eV, 1.41 eV and 1.60 eV, respectively. Compared to BCHYYb, BSCHYYbHo electrolyte has higher proton concentration and proton transference number. Overall, BSCHYYbHo ceramic with dense structure and high proton transference number is a potential material for application.

Structural, electronic, elastic, and optical properties of chalcogenide perovskite SrZrS3 under ambient and high-pressure conditions

Hydrostatic pressure is an effective tool that can give rise to novel crystal structures and physical properties. In this paper, we perform the first-principles calculation based on density-functional theory (DFT) to study the structural, electronic, elastic, and optical properties of chalcogenide perovskite SrZrS3 under pressure. The results indicated that both the lattice constant and cell volume decrease with the increase of pressure, which are matched well with available previous values. The obtained elastic constants reveal the SrZrS3 is mechanically stable between 0 and 15 GPa. Additionally, the main features of the valence and conduction bands have been analyzed from the total and partial density of states. The complex dielectric function, refractive index, absorption coefficient, reflectivity, and the extinction coefficient are also calculated and analyzed. According to our work, we found that the optical properties of SrZrS3 undergo a red shift with increasing pressure.

The impact of Sm substitution on structural and optical properties of LaFeO3: their application as a photocatalyst for the degradation of methylene blue under visible light irradiation

The objective of the present study is to enhance the photocatalytic activity of LaFeO3 by inserting Sm ions on the La site for the degradation of methylene blue. We employed citric sol–gel techniques to produce ultrafine powders of the La1-xSmxFeO3 (0.0 ≤ x ≤ 0.5) nanoperovskite samples. All samples confirmed the presence of a pure Pbnm orthorhombic phase structure. The decrease of lattice constants, crystallite sizes and cell volumes, and increase in microstrains suggest a deformation of the structure due to the addition of Sm ion on the La site of the La1-xSmxFeO3. The images of HR-TEM and FE-SEM for all samples revealed a homogeneous distribution of almost spherical nanoparticles, with decreasing average particle sizes ranging from 49.95 ± 3.12 to 34.28 ± 4.38 nm, as Sm ratios increases from 0.0 to 0.5%. The spectra of FTIR confirmed the formation of a Lax-1SmxFeO3 perovskite phase by the appearance of lower frequency bands Fe–O-Fe and La-O-La at ∼ 400 cm−1 and a higher absorption band Fe -O and La -O at ∼ 564 cm−1. The Raman spectra were employed to investigate the formation of phonon modes of La1-xSmxFeO3. Diffused reflectance spectroscopy (DRS) demonstrated the decrease of energy gap (Eg) values from 2.38 to 1.86 eV and the increase in Sm content from 0.0 to 0.5%. Since these Eg values fall within the visible light region, the photocatalytic activity of La1-xSmxFeO3 samples demonstrated a gradual increase in the degradation ratio of MB from 31.7 to 73.2% with increasing Sm content from 0.0 to 0.5%, respectively, under visible light illumination.

First-principles calculations to investigate mechanical, thermoelectric and optical performance of inorganic double perovskites Rb2CuBiX6 (X = Cl, Br, I) for energy harvesting

The double perovskites Rb2CuBiX6 (X = Cl, Br, I) are studied for thermoelectric and optoelectronic applications for energy harvesting. The confirmation of thermodynamic constancy has been reported by formation energy and tolerance factor by structural stability. The lattice constant increases and bulk modulus decreases by changing the halogen ions (Cl, Br, I). The ductile behavior, large Debye and Kelvin temperatures along hardness and ultralow values of lattice thermal conductivity are calculated from elastic constants. The TB-mBJ potential has been used to modify the band gaps from 1.18 to 0.68 eV by shifting of halogen ions Cl to I. The optical characteristics are analyzed by absorption, dispersion, refractive index, and reflection of light energy. In addition to above, the transport characteristics are analyzed by Seeback coefficient, electronic and thermal conductivities. The figure of merit calculations shows the excellent thermoelectric performance of studied DPs.

First-principle calculations of structural and optoelectronic properties of wurtzite Zn1-x-yBexMgyO quaternary alloys closely lattice matched to the ZnO substrate for UV-A optoelectronic applications

Structural and optoelectronic properties of some wurtzite Zn1-x-yBexMgyO quaternary alloys closely lattice-matched to w-ZnO substrate are investigated with density functional theory. The Zn0·75Be0·0625Mg0·1875O, Zn0·6875Be0·0625Mg0·25O and Zn0·625Be0·0625Mg0·3125O alloys having Be/Mg composition ratio in the experimentally prescribed range 2.0–4.0 are considered to achieve high quality stable wurtzite quaternary crystals. Lattice constants (a0, c0) decrease, while direct band-gap (Γ-Γ) increases with increasing Be and Mg composition sum. These optically anisotropic quaternary alloys exhibit diverse optical properties due to electronic transitions from valence O-2p to Be-2p, Be-3s, Zn-5s, Mg-4s, Mg-3p states of conduction band. Calculated optical energy gap, slightly higher than band-gap, shows blue shift with increasing Be and Mg composition sum. Calculated static optical constants ε1(0), n(0), R(0) of these alloys reduce with increasing band-gap and vice versa. These quaternary alloys with band-gaps, fundamental absorption edges and optical energy gaps in the UV-A region would have potential applications in fabricating UV-A optoelectronic devices.

Exploring the influence of rare earth ions at A-site on the properties of LnBaCo2O5+δ cathode for solid oxide fuel cells

The influence of rare earth ions on layered perovskite (AA'B2O5+δ) is the key to the development of highly active layered perovskite cathode. Herein, we make a systematic explanation through experiment and first-principles calculation. The lattice constant decreases with the decrease of Ln3+ ionic radius, resulting in a smaller space of interstitial oxygen position and increasing oxygen Frenkel energy. The electrochemical activity of LnBaCo2O5+δ (Ln = Pr, Nd and Sm) electrodes decreases with the decrease of Ln3+ ionic radius, which is mainly attributed to a lower oxygen Frenkel energy. Electrochemical impedance spectra tests show that there are significant differences in the surface exchange process of oxygen because of different surface oxygen vacancy concentration for LnBaCo2O5+δ. For Ln = Pr, Nd, and Sm cathodes, the maximum power densities of the anode-supported Ni-YSZ/YSZ/GDC/LnBaCo2O5+δ single cells reach 1.48, 1.36 and 1.06 W/cm2 at 800 °C, respectively, indicating that PrBaCo2O5+δ with the maximum rare earth ion radius exhibits better oxygen reduction reaction. These findings provide guidance for the design and fabrication of highly active layered perovskite electrode materials.

Enhanced thermoelectric properties of porous hybrid ZnSb/EG-treated PEDOT:PSS composites

We adopt a new feasible strategy to fabricate hybrid inorganic-organic composites by soaking ZnSb in EG-treated PEDOT:PSS solution. The pristine ZnSb and the hybrid ZnSb/EG-treated PEDOT:PSS composites are characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), Hall measurements, electronic transport and thermal transport. The compositing effects of this hybrid material system include a decrease in lattice constants, an increase in bulk density, and a decrease in porosity with increasing soaking days. As a result, the hybrid ZnSb/EG-treated PEDOT:PSS composite with a soaking time of 30 days has a higher power factor and lower thermal conductivity than that of the pristine ZnSb. This results in an improvement in the magnitude of zT with zT = 0.71 at 525 K.

Effects of pressure on structural, mechanical, and electronic properties of chalcopyrite compound CuAlS2

First-principles method is performed to investigate the structural, electronic, elastic and mechanical characteristics of the tetragonal CuAlS2 in the pressure range from 0 to 10 GPa. The results indicated that both the lattice constant and cell volume decrease with the increase of pressure, which are matched well with available previous values. The pressure has a more significant influence on the c direction than the a and b direction. The obtained elastic constants reveal the tetragonal CuAlS2 is mechanically stable between 0 and 10 GPa. The bulk, shear, and Young’s modulus are evaluated by Voigt-Reuss-Hill approximation. All these elastic moduli exhibit a monotonic feature as a function of pressure. The Poisson’s ratio, Pugh’s criterion, and Cauchy pressure indicate that ternary chalcopyrite semiconductor CuAlS2 is ductile against pressure. Meanwhile, the analysis of the electronic structures reveals that the states near the valence band top are derived from Cu 3d and S 3p orbitals, and the lowest conduction band is composed of Al 3p and S 3p orbitals. We expect that the findings predicted the physical properties of this compound will promote future experimental studies on CuAlS2.

Successive, overlapping transitions and magnetocaloric effect in Te doped Ni-Mn-Sn Heusler alloys

Ni 43Mn 46Sn11−xTex (x = 0.1, 0.2, 0.3, 0.4, 0.5, 1) alloys have been prepared by arc melting. Structural studies show the presence of L21 cubic austenite phase. With the increase in Te concentration, the martensite phase evolves and the lattice constant decreases. Magnetic studies show that all the alloys exhibit first-order phase transition. It has been observed that the martensite temperature increases successively with the increase in Te concentration. A non-linear variation of magnetic entropy change, thermal hysteresis was observed in the alloys with increase in Te concentration. Magnetocaloric effect has been observed over a broad range of temperature span from 215 K to 289 K by varying the Te concentration. The magnetocaloric properties with Te doping have been analysed by using quantitative approach. Successive transitions and overlapping magnetocaloric effect occur with Te doping and they can be harnessed as layered magnetocaloric materials to enhance the refrigeration capacity. Our studies manifest that the martensite temperature and magnetocaloric properties are tuneable with the Te concentration and hence can be useful for magnetic refrigeration applications.

Co-Sputtering Crystal Lattice Selection for Rare Earth Metal-Based Multi Cation and Mixed Anion Photochromic Films

Rare-earth oxyhydride (ReOxHy) films are novel inorganic photochromic materials that have strong potential for applications in windows and optical sensors. Cations greatly influence many material properties and play an important role in the photochromic performance of ReOxHy. Here we propose a strategy for obtaining Gd1-zYzOxHy films (z = 1, 0.7, 0.5, 0.4, 0.35, 0.25, 0.15, 0) using one-step direct-current (DC) magnetron co-sputtering. Distinct from the mixed anion systems, such material would belong to the class of mixed anion and mixed cation materials. For Gd1-zYzOxHy films, different co-doping ratios can help tune the contrast ratio (that is, the difference between coloration and bleaching transmittance) and cycling degradation, which may be related to the lattice constant. X-ray diffraction (XRD) patterns show that the lattice constant increases from 5.38 Å for YOxHy to 5.51 Å, corresponding to Gd0.75Y0.25OxHy. The contrast ratio, in particular, can be enhanced to 37% from 6.3% by increasing the lattice constant, directly controlled by the co-sputtering power. When the lattice constant decreases, the surface morphology of the sample with the smallest lattice constant is essentially unchanged by testing in air with normal oxidation for 100 days, suggesting great improvement in environment durability. However, the crystal structure cannot be overly compressed, and co-sputtering with Cr gives black opaque films without photochromic properties. Moreover, because the atomic mass of different rare earth elements is different, the critical pressure p* (films deposited at p < p* remain metallic dihydrides) is different, and the preparation window is enlarged. Our work provides insights into innovative photochromic materials that can help to achieve commercial production and application.

Effect of Lattice Constants and Precipitates on the Dimensional Stability of Rolled 2024Al during Isothermal Aging

The change in material dimensional will lead to the decline of instrument accuracy and reliability. In this paper, the characterization and analysis of the lattice constant, precipitates, and dislocation density of the material by X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveals the reason why the relative dimensional change in the rolled 2024Al is one order of magnitude lower than that of the as-cast 2024Al during isothermal aging. Compared with as-cast 2024Al, the dislocation density of rolled 2024Al is higher, the lattice constant decreases less before and after aging, and the precipitates have orientation and more content, resulting in the dimensional change in rolled 2024Al being smaller than that of as-cast 2024Al. In addition, two main reasons for decreasing the dimensional change in rolled 2024Al are discussed: the decrease in lattice constant, the formation and growth of the S phase before and after aging.

Red shift of lead-free halide perovskite RbCaCl3 under pressure for enhancing optoelectronic performance

This study focuses on the exploration of pressure effects on the structural, electronic, optical, and mechanical properties of a cubic halide perovskite RbCaCl3 using density functional theory. The calculated values of lattice constant and unit cell volume at zero pressure are justified by the previous experimental and theoretical studies. As pressure is applied both the lattice constant and unit cell volume decrease steadily because of bond length reduction inside the material. The indirect band gap nature of the studied perovskite transforms into direct under applied pressure of 40 GPa and more. Moreover, the band gap value significantly reduces under pressure effect from ultraviolet to visible energy region. Though the bonding nature of both Rb−Cl and Ca−Cl is initially ionic, the induced pressure slightly reduces the ionicity of Rb−Cl and makes the Ca−Cl bond covalent. The optical absorption reveals a red shift in the visible energy region advantageous for using RbCaCl3 in solar cell applications. In addition, the overall optical analysis reveals that the pressure-induced compound is more suitable for optoelectronic device applications than that of zero pressure system. The external hydrostatic pressure significantly affects the mechanical properties of titled compound, making it more ductile and anisotropic.

Effect of rare earth doping on magnetic and dielectric properties of NiZnMn ferrites

In present work, RE0.01Ni0.3Zn0.4Mn0.3Fe2O4 (RE=Fe, La, Nd, Sm, Gd, Dy, Yb) ferrites with strictly controlled main composition were prepared. X-ray diffraction analysis shows that the lattice constant decreases with the increase of atomic number of rare earth. The infrared spectra demonstrate the changes of tetrahedral and octahedral bonds. The saturation magnetization is about 74 emu/g and initial permeability is about 120 for undoped ferrite. They decrease slightly after rare earth doping, but the impact of different rare earth on Ms is same. The Curie temperature of almost all samples is 262 ℃. Zero field cooling-field cooling curves demonstrate the existence of spin glass state or superparamagnetism at high temperature. Sm, Gd and Dy doped ferrites have special dielectric properties with more relaxation processes. Appropriate rare earth doping greatly improve the cut-off frequency, dielectric constant for MHz device materials and dielectric loss for GHz electromagnetic wave absorption materials.

Effect of B substitution for Si on the electronic structure and magnetic properties of Heusler alloys Fe2CoSi1-xBx (x = 0–0.25)

A series of Fe2CoSi1-xBx (x = 0, 0.05, 0.1, 0.15, 0.2 and 0.25) Heusler alloys has been synthesized using melt-spinning method, which can help to reduce the precipitation of the secondary phase and form a highly ordered structure. The XRD patterns indicate that, when x = 0–0.1 the Fe2CoSi1-xBx melt-spun ribbons are single Heusler phases, but when x = 0.2 and 0.25 a small amount of secondary phase appears. The lattice constant decreases with increasing B content, suggesting that B mainly enters the substitutional sites of Si. The Curie temperatures TC of Fe2CoSi1-xBx alloys are all higher than 1000 K, and a 21 K increase of TC is observed as x varies from 0 to 0.25. The hysteresis loops of Fe2CoSi1-xBx alloys show soft magnetic character. Their saturation magnetizations Ms at 5 K and 300 K are similar and close to 5μB / f.u. The zero-gap half-metallic character reported for Fe2CoSi has been confirmed in present work. But with the substitution of B for Si, the Fermi level moves from the center in Fe2CoSi DOS to the left edge of the minority energy gap in Fe2CoSi0.75B0.25, which may disturb the half-metallic character when B content is high. When × = 0–0.1, the Ms at 5 K of Fe2CoSi1-xBx agree well with the calculated total spin moments, but when the B content is high, especially when x = 0.2 and 0.25, a deviation between the experimental and theoretical results is observed, which is related to the secondary phase in these samples.

Engineering electronic structures of Janus monolayer group-III monochalcogenides via biaxial strain

We investigate the effects of biaxial strain and spin-orbit coupling on the electronic structures of Janus monolayer group-III monochalcogenides based on first-principle calculations. Due to the spin-orbit coupling and mirror symmetry breaking, Rashba band splitting appears at Γ point of the bottom conduction band and the band gap decreases significantly. The spin-orbit coupling strength and electronic structures can be greatly tuned by biaxial strain, which originate from the change of interaction between pz orbitals. As the lattice constant decreases, the interaction between pz orbitals is enhanced, leading to the decrease (increase) of the energy of corresponding bonding (anti-bonding) state, which is the origin of the indirect-direct-indirect transition of the band gap. In addition, when tensile strain is applied, the pz orbital component of Te atoms increases, leading to the enhancement of the Rashba effect. These results are of great significance for the band engineering and spin-orbitronics of two-dimensional materials.

The experimental and theoretical study of Al doped ZnSn(OH)6 to improve gas sensitivity

The cubic ZnSn(OH)6 and Al@ZnSn(OH)6 were fabricated via hydrothermal method and detected by XRD, SEM, TEM, SAED, EDS and XPS technologies. XRD results show that the as-prepared sample is ZnSn(OH)6 and has good crystallinity. After doping Al, the lattice constant decreases and the (200) peak shifts to the right. SEM images display that the obtained samples are cubic lacking edges and corners, and have stepped stripes on the surface with a size of about 0.5–1 µm. XPS results reveal that the sample contained Zn, Sn and O. And O 1 s has three peaks of lattice oxygen, vacancy oxygen and chemisorption dissociated oxygen. The experimental results illustrate that the sensitivity of ZnSn(OH)6 to ethanol is obviously improved after doping Al element, and the optimal working temperature becomes lower. The resistance of ZnSn(OH)6 decreases to about 1/13 under 240 ℃. The molar ratio of Sn or Zn to NaOH will affect the crystal orientation and thus affect the morphology of ZnSn(OH)6. The calculation results show that the donor impurity level will be formed at the band bottom when Al doping ZnSn(OH)6. Which could further explain why the carrier concentration increases and the material resistance decreases after Al doping.

Theoretical simulation structural, elastic, electronic, optical, vibrational and thermal properties of AgGaxIn1-xS2 (x = 0, 0.25, 0.5, 0.75, 1)

The elasticity, vibration and thermodynamic properties of single crystal materials are very important in the field of laser and nonlinear optics. Therefore, it is very important to understand the physical mechanism of thermal properties in such systems. In this work, the structural, elastic, vibrational and thermodynamic properties of the AgGaxIn1-xS2 (x = 0, 0.25, 0.5, 0.75, 1) have been performed systematic within generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE). The results show that the AgGaxIn1-xS2 series have similar physical properties. When Ga concentration increases gradually, the lattice constants (a and c) decrease drastically with the increase of Ga content x. The polycrystalline elastic moduli including bulk modulus B, Young's modulus E, shear modulus G and Poisson's ratio v have also been successfully calculated. The brittle and ductile properties were judged by using B/G and Poisson's ratio. The anisotropy was characterized by calculating several different anisotropic indexes and the 3D figures of directional dependences of reciprocals of bulk modulus. Use the hybrid functional HSE06 to study the electronic properties of AgGaxIn1-xS2, and suggest that the HSE06 hybrid functional can obtain a more reasonable band. In addition, the optical spectrum are derived and main spectral features are interpreted in terms of the electronic structure. The calculated results of vibrational characters indicate that AgGaxIn1-xS2 (x = 0, 0.25, 0.5, 0.75, 1) are dynamic stability as increasing of Ga concentration from 0.0 to 1. Finally, the thermodynamic properties related to phonons have been realized and explored.

Enhanced low-field magnetocaloric effect in Dy-doped hexagonal GdBO3 compounds

Borates have attained increasing attention attributed to their excellent thermal stability, distinctive thermodynamic property, and high mechanical strength in recent years. A series of polycrystalline Dy-doped GdBO3 compounds was prepared, their crystal structures, magnetic properties, and cryogenic magnetocaloric effects were comprehensively investigated. The compounds crystallize in hexagonal structure (space group P63/mmc), the lattice constant decreases with the increase of Dy content. Dy-doping in GdBO3 significantly reduces critical magnetic field and enhances low-field magnetocaloric effect. The maximum magnetic entropy changes for the Gd1–xDyxBO3 (x = 0.6, 0.8, and 1) compounds in a field change of 2 T surpass 17.3 J/(kg·K) at 2.5 K, enhanced by nearly 120% compared to GdBO3 (8.0 J/(kg·K)). Besides, the corresponding refrigeration capacity increases from 33.9 to 62.2, 57.2, and 72.5 J/kg, respectively, with an enhancement of 70%–110%. The considerable maximum magnetic entropy change, refrigerating capacity, and temperature averaged entropy change make them competitive candidates for cryogenic magnetic refrigeration.

First-Principles Prediction of Structural, Elastic, Mechanical, and Electronic Properties of Cu2ZnSnS4 under Pressure

Quaternary compounds are high desirable for realizing advanced optoelectronic and spintronic devices. In this paper, we have systematic studied the effects of pressure on the structural, elastic, mechanical, and electronic properties of Cu2ZnSnS4 by means of first-principles calculations. The results indicated that both the lattice constant and cell volume decrease with the increase of pressure, which are matched well with available previous values. The pressure has a more significant influence on the c direction than the a and b direction. The obtained elastic constants reveal the Cu2ZnSnS4 is mechanically stable between 0 GPa and 15 GPa. The bulk modulus, shear modulus, and Young’s modulus are evaluated by Voigt-Reuss-Hill approximation. All these elastic moduli exhibit a monotonic feature as a function of pressure. The Poisson’s ratio, Pugh’s criterion, and Cauchy pressure indicate that the quaternary compound Cu2ZnSnS4 is ductile against pressure. Meanwhile, the analysis of the electronic structures reveals that the states near the valence band top are derived from Cu 3d and S 3p orbitals, and the lowest conduction band is composed of Sn 5s and S 3p orbitals. We expect that the findings predicted the physical properties of this compound will promote future experimental studies on Cu2ZnSnS4.

Effect of heat-treatment time on microstructure and tribological behavior of (TiVCrAlMo)N high-entropy alloy films

In this work, the effect of heat-treatment time (0 h, 2 h, 4 h, and 8 h) at 300 °C on the microstructure and tribological properties of (TiVCrAlMo)N high-entropy alloy (HEA) films are studied in detail. The results indicate that the HEA films with and without heat-treatment are all composed of a single FCC solid solution phase. With the increase of heat-treatment time, the lattice constant decreases gradually but the surface roughness has a tendency to increase, however, the microhardness and tribological properties don't show a linear relationship. The HEA film with 2 h heat-treatment has a relatively low micro-hardness, but the lowest friction coefficient (~0.22) with the best wear-resistance, while the HEA film with 8 h heat-treatment has the highest micro-hardness, but has the worst wear-resistance. The lowest friction coefficient of HEA film with 2 h heat-treatment is mainly due to the highest content of the MoO3 self-lubricating phase. Moreover, owing to the different micro-hardness and the different surface formation with different heat-treatment times, the wear mechanisms of these HEA films are quite different.