Lattice Constant Decreases Research Articles

Synergistic effects of liquid phase sintering and B-site substitution to enhance proton conductivity of BaZr0.1Ce0.7Y0.1Yb0.1O3-δ for protonic ceramic fuel cell

This paper is dedicated to improving the sintering and conductivity of BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) by adding ZnO-CuO dual-sintering aids. The synergistic effects of liquid-sintering of Zn and B-site substitution of Cu on the sinterability and proton conductivity of BZCYYb are systematically investigated. X-ray diffraction (XRD) analysis of BZCYYb after addition of ZnO-CuO (BZCYYb-Zn-Cu) confirms the complete perovskite phase formation without any secondary phase. The substitution of Ce4+ (0.87 Å) with Zn2+ (0.74 Å) or Cu2+ (0.73 Å) induces a shift in XRD diffraction peak to higher angle due to a decrease in lattice constant. Energy dispersive X-ray spectroscopy analysis indicate a distinct distribution of Zn primarily at the grain boundaries, while Cu is predominantly located within the grains of BZCYYb-Zn-Cu. The addition of ZnO-CuO into BZCYYb results in a denser microstructure with larger average grain size. Furthermore, the substitution of Ce4+ by Cu2+ increases the concentration of oxygen vacancies and reduces activation energy. For BZCYYb-Zn-Cu, the proton conductivity reaches 4.52×10-2 S/cm at 750 °C, approximately 3 times higher than that of BZCYYb. This enhancement can be attributed to the synergistic effects of larger average grain size resulting from liquid phase sintering of Zn, low active energy, and high concentration of oxygen vacancies arising from Cu B-site substitution. BZCYYb-Zn-Cu is used as the electrolyte for anode support SOFC, and the single cell exhibits remarkable electrochemical performance and excellent stability in H2 fuel. This research establishes a crucial theoretical foundation for the preparation and performance evaluation for large-size protonic ceramic cell.

Effect of cryogenic treatment time on mechanical properties of Sm2Co17 permanent magnets

Sm2Co17 permanent magnets are widely used in aerospace, radar communication, rail transit, and various other fields. However, their brittleness restricts their application. Improving their mechanical properties is of practical interest. Cryogenic treatment can be used as a means to enhance the mechanical properties of Sm2Co17 permanent magnets. However, the specific relationship between cryogenic treatment time and the properties of samarium-cobalt magnets has not yet been fully understood. In light of this, this paper focuses on exploring the influence of cryogenic treatment time on the mechanical properties of Sm2Co17 permanent magnets, aiming to provide a foundation for further elucidating this relationship. The results show that the mechanical properties can be significantly affected by cryogenic treatment time, with the flexural strength and elastic modulus increasing by 27.6 % and 9.6 % respectively when 3 h of treatment. However, the effect of further extending the treatment time to 6 h is not significant. In addition, the cryogenic treatment time has no adverse effect on magnetic properties. Additional analysis reveals that the enhancement in mechanical properties is primarily attributed to the decrease in residual stress and lattice constants. This study provides valuable insights into optimizing cryogenic treatment parameters to enhance the mechanical performance of Sm2Co17 permanent magnets while preserving their magnetic properties.

Enhancing electromagnetic properties of NiCuZn ferrites through Nb and Li Co-doping for wireless power transfer

With the rapid development of wireless charging technology, there is a growing demand for ferrite materials with high permeability, high saturation magnetic induction intensity, and low power loss. This study aims to enhance the electromagnetic performance of NiCuZn ferrite by co-doping Nb5+ and Li+. The influence of the doping levels Nb5+ and Li + on the morphology, crystal structure, and electromagnetic properties of NiCuZn ferrite were studied in detail. Structural analysis shows that the lattice constant decreases as the Nb5+-Li+ doping concentration increases, and the NiCuZn ferrite exhibits a high density and homogeneous microscopic morphology at the optimum concentration of x = 0.004. Specifically, at a doping concentration of x = 0.004, the magnetic permeability at 1 MHz measured at 1112.1, the saturation magnetic induction intensity reached 458.98 mT, and the power loss was minimized to 521.85 kW/m3, demonstrating significant improvement in the transmission power of wireless charging applications.

Tunable ferromagnetism via in situ strain engineering in single-crystal freestanding SrTiO3-δ membrane

Engineering stoichiometry and lattice field in transition metal oxides (TMOs) is recognized as a promising approach for achieving emergent functional properties and exploring fundamental scientific questions. To overcome the constraints of rigid epitaxial TMOs, this study releases and transfers freestanding SrTiO3-δ (STO3-δ) membranes, derived using a water-dissolution method from STO3-δ/Sr3Al2O6/SrTiO3, onto flexible polyimide. In-plane mechanical strains were then applied to investigate the strain evolution-induced ferromagnetism. Continuous strain modulates interplane and intraplane exchange interactions between neighboring atoms in the ferromagnetic STO3-δ membranes, thereby influencing their ferromagnetic properties. STO3-δ initially undergoes in-plane octahedral distortion when strain is less than 1.5 %, followed by a decrease in the out-plane lattice constant. This structural variation leads to complex strain-dependent behaviors in the saturation magnetic moment (Ms) and coercive field (Hc) of STO3-δ, with Ms and Hc exhibiting a nonlinear, volcano-shaped, and step-wise correlation, respectively. Our research demonstrates that freestanding STO3-δ serves as a platform for studying local defects and their impacts on tunable magnetic properties, greatly enhancing our understanding of t2g electron engineering through modulable inter/intra plane exchange coupling with lattice field.

Effects of Sm and Gd co-doping on ionic conductivity of ceria-based electrolyte materials

This study explores the impact of co-doping on ceria-based electrolyte materials with samarium (Sm) and gadolinium (Gd) to improve their structural, morphological, and ionic conductivity properties synthesized through a co-precipitation technique using sodium hydro-oxide (NaOH) as the precipitating agent for solid oxide fuel cell (SOFC) applications. The aforementioned approach provides benefits like uniformity, high purity, and simplicity of synthesis. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the crystal structure and morphology of the synthesized materials. No secondary phases were observed revealing the phase purity of the material. A decrease in lattice constant was detected due to the replacement of a small concentration of Gd with Sm having small ionic radii compared to Sm. Homogeneity and decrease in particle size of prepared samples were observed via SEM analysis predicting the enhancement in the grain size with the reduction in grain boundaries and elemental composition through EDX agreed with the starting composition. Impedance spectroscopy was employed to measure the ionic conductivity of the electrolyte samples. Our results demonstrate a significant decrease in grain and grain boundary resistances causing the increase in ionic conductivity with the introduction of Gd and Sm as co-dopants into the ceria structure. The optimal doping concentration was found to be 10 % Gd and 10 % Sm. The co-doped ceria had a high ionic conductivity of 6.28 × 10−2 S/cm at 750οC and a low activation energy of 0.44 eV, indicating improved ionic mobility. This study provides valuable insights into the role of Gd and Sm co-doping in enhancing the ionic conductivity of ceria-based electrolyte materials, which is crucial for the advancement of high-performance SOFCs.

Pressure effect on the structural, electronic, mechanical, optical and thermal properties of Ga2TiX6 (X = Cl, Br): A DFT simulation

The pressure effect on the physical properties of Ga2TiX6(X = Cl, Br) has been carried out through density function theory (DFT) accomplished via CASTEP guidelines. At ambient condition the structural aspects of Ga2TiX6(X = Cl, Br) show well accord with the previous theoretical data. A dramatically decrease of lattice constants, cell volumes and bond length with pressure is perceived. The negative enthalpy energy ensured the chemical formation of Ga2TiX6(X = Cl, Br). The positive stiffness constants (Cij) ensure the mechanical stability of Ga2TiX6(X = Cl, Br) at ambient and hydrostatic pressure. Moreover, the fundamental polycrystalline factors of phases Ga2TiX6(X = Cl, Br) such as bulk, shear and Young’s moduli, Poisson’s and Pugh’s fraction, machinability index as well as hardness of these materials have been calculated and discussed at ambient and hydrostatic pressure. Having very low values of bulk modulus (<100 GPa) they can be considered as soft materials. The increase of machinable index with pressure ensure the high lubricating properties, low friction, and high plastic strain of Ga2TiX6(X = Cl, Br) and also ensure their possible industrial applications. Band structure analysis ensure the semiconducting nature of Ga2TiX6(X = Cl, Br) at ambient condition but the semiconducting nature shift to metallic manner at 55 GPa and 65 Gpa respectively. The decrease of total density of states is observed at high pressure. The creation of new bond at high pressure is also observed in materials Ga2TiX6(X = Cl, Br). The investigated optical features ensured that the studied phases can be used in UV photodiodes, and UV light emitters since they revel intense peaks at UV region. Very low Debye temperature, melting temperature and thermal conductivity are observed at ambient condition which ensures that the compounds Ga2TiX6(X = Cl, Br) can be used as thermal barrier coating materials (TBC).

Investigating structural and optoelectronic properties of Cr-substituted ZnSe semiconductors

The optoelectronic and structural characteristics of the Zn1−xCrxSe (0 ≤ x ≤ 1) semiconductor are reported by employing density functional theory (DFT) within the mBJ potential. The findings revealed that the lattice constant decreases with increasing Cr concentration, although the bulk modulus exhibits the opposite trend. ZnSe is a direct bandgap material; however, a change from direct to indirect electronic bandgap has been seen with Cr presence. This transition is caused by structural alterations by Cr and defects forming, which results in novel optical features, including electronic transitions. The electronic bandgap decreases from 2.769 to 0.216 eV, allowing phonons to participate and improving optical absorption. A higher concentration of Cr boosts infrared absorption and these Cr-based ZnSe (ZnCrSe) semiconductors also cover a wider spectrum in the visible range from red to blue light. Important optical parameters such as reflectance, optical conductivity, optical bandgap, extinction coefficient, refractive index, magnetization factor, and energy loss function are discussed, providing a theoretical understanding of the diverse applications of ZnCrSe semiconductors in photonic and optoelectronic devices.

Impact of boron substitution on the thermoelectric, mechanical stability, electronic and optical properties of InP alloys

Density Functional Theory (DFT) calculations, utilizing the full potential linearized augmented plane wave (FP-LAPW) method, were performed to investigate the effect of boron (B) substitution on the InP system through GGA and mBJ-GGA formalisms, aiming to improve its band gap energy. Lattice equilibrium optimization determined that the stable structure of the alloys at equilibrium energy shows a decrease in lattice constants with increasing boron concentration (x). The calculated formation enthalpies, which are negative, indicate that these systems are experimentally synthesizable. The elastic analysis confirms that the doped alloys are elastically stable and exhibit ductile properties. The optical parameter analysis reveals that the optical energy loss functions are minimal or zero in the infrared, visible, and ultraviolet ranges, suggesting their suitability for optical applications across these energy ranges. Specifically, the band gaps were found to range from 0.878 eV for x = 0.25–1.920 eV for x = 0.75 using the mBJ-GGA formalism. Furthermore, the role of B-doping in the InP system for thermoelectric technology was systematically investigated, revealing that our alloys possess good thermoelectric properties with a figure of merit (ZT) reaching up to 0.7 for x = 0.75. These results demonstrate that accurate tuning of the energy band gap through doping is an effective technique for discovering novel materials suitable for both thermoelectric and optoelectronic applications.

Investigating stress-induced effects on the multifaceted properties of cubic NaTaO3 perovskite oxide: prospects for advanced applications

This study explored the structural, optoelectronic, elastic, mechanical, and thermodynamic behaviour of NaTaO3 cubic perovskite oxide, under varying stress levels. Geometric property analysis reveals a decrease in lattice constants from 4.1 Å to 3.7 Å and cell volume from 71.1–53.4 Å3 as stress increases from 0 to 100 GPa. X-ray diffraction analysis indicated the stable cubic phase with slight peak shifts, demonstrating the material's structural flexibility. Electronic properties revealed an initial increase in the band gap (1.698 eV to 1.936 eV) with applied stress up to 60 GPa, which could be attributed to complex interactions within the material's electronic structure. Optical property analysis suggested that NaTaO3 possessed high optical absorption and conductivity, along with low reflectivity. Furthermore, elastic constants meeting the Born-stability condition (C11 – C12 > 0, C11 + 2C12 > 0, and C44 > 0) confirm the material's mechanical stability. Additional characteristics like the Poisson ratio, Cauchy pressure, and Frantsevich ratio highlighted the ductile and anisotropic nature of NaTaO3. Thermodynamic and phonon dispersion analysis suggested that NaTaO3 can withstand high-stress levels, evidenced by its elevated Debye temperature, indicating superior mechanical stability and increased resistance to thermal degradation. Based on these findings, NaTaO3 proposed as a potential candidate for photovoltaic and thermoelectric devices.

Effects of Ni2+ modified La0.67Ca0.33MnO3 ceramics on their temperature coefficient of resistivity and magnetoresistance properties

Element-modified La0.67Ca0.33MnO3 (LCMO) ceramics have been a major research subject in the past decades due to their various electromagnetic properties and potential applications in infrared detection and magnetic storage devices. However, its electromagnetic transport mechanism has not been fully elucidated and its properties need to be further optimized for practical applications. Here, we report the effect of Ni2+ doping on the structural, magnetic, the temperature coefficient of resistivity (TCR) and magnetoresistance (MR) properties of La0.67Ca0.33Mn1-xNixO3 (LCMNO) ceramics. All samples were synthesized by the sol-gel method and were in pure phase. XRD refinement results show a decrease in lattice constants and cell volume of LCMNO ceramics with increasing Ni2+ content. The XPS study confirms the reduction of the Mn3+/Mn4+ ratio and indicates that oxygen vacancies occur in LCMNO ceramics due to the Ni2+ doping. Curie-Weiss fitting results suggest ferromagnetic superexchange coupling between Ni2+ and Mn3+(4+) ions. The electrical transport properties of LCMNO ceramics were further investigated using the spin polaron hopping model in the high temperature range and the various competing scattering mechanisms in the low temperature range. In addition, double resistivity peak behavior is observed at x = 0.04 and 0.05. Furthermore, the TCR of the LCMNO ceramics increased to 45.4 %·K−1 (x = 0.01), while the MR increased to 67.9 % (x = 0.03), respectively. Our studies contribute to a better understanding of the electromagnetic properties of LCMNO ceramics.

Study on hydrogen storage properties of Ti–V–Fe–Mn alloys by modifying Ti/V ratio

The high stability of hydride phase has limited the improvement for the hydrogen storage properties of Ti–V based alloy at room temperatures. In this work, the stability of hydride was reduced by designing a low-price Ti–V–Fe–Mn alloy, and the effect of Ti/V ratio on the crystal structure and hydrogen storage properties was systematically investigated. The Ti40-xV40+xFe15Mn5 (x = 0, 2, 4, 6, 8) alloys were synthesized using arc melting, and the as-prepared alloys are all composed of single BCC phase. The lattice constant and cell volume decrease linearly with a lessening in Ti/V ratio. The reduction of cell volume makes it difficult for hydrogen atoms to diffuse, resulting in a sluggish hydrogen absorption rate. The dehydrogenation plateau in PCI curve rises and corresponding thermodynamics is optimized with a decrease in the lattice constant, and the hydrogen atoms are more readily to release, especially for Ti32V48Fe15Mn5 alloy with the dehydrogenation capacity of 1.83 wt% at 373 K. The result indicates the thermodynamic properties can be optimized by adjusting the lattice constant of Ti–V–Fe–Mn alloys, and hydrogen storage capacity is improved effectively. This study provides a reference for composition design of Ti–V–Fe–Mn alloys for high-density hydrogen storage.

Investigation of the crystal-oriented behavior of rare earth substituted Sr2NaNb5O15 lead-free piezoelectric materials under a high magnetic field

The crystal-orientation behavior of Sr2NaNb5O15 (SNN) lead-free piezoelectric materials under a magnetic field was investigated by substituting rare-Earth elements (Ln = Nd, Eu, Ho, Yb), which were selected based on their ionic radii and magnetic or non-magnetic ions. The magnetic ions, Nd, Ho, and Yb, did not affect the magnetic anisotropy of the SNN. The nonmagnetic ions (Eu3+) changed from the a, b-axis orientation to the c-axis orientation in the direction of the magnetic field. The Eu-substituted SNN powders revealed that the degree of orientation of the c-axis increased as the Eu content increased. Consequently, c-axis-oriented Eu-substituted SNN ceramics were obtained with the degree of orientation of 0.9. The diamagnetism along the a, b-axis became larger than that along the c-axis owing to a decrease in the c-axis lattice constant. By substituting Eu with SNN, the piezoelectric properties decreased as the hardening of SNN progressed.

Structural, Elastic, Mechanical, Electronic, and Optical Properties of a Novel Quaternary Chalcogenide Semiconductor Ba3GeTeS4

The structural, elastic, mechanical, electronic and optical properties of Ba3GeTeS4 have been studied by pseudopotential density functional theory static calculations. The results indicated that both the lattice constant and cell volume decrease with the increase of pressure, which match well with available previous values. The pressure has a more significant influence on the b direction than the a and c direction. The obtained elastic constants reveal that Ba3GeTeS4 is mechanically stable between 0 GPa and 20 GPa. The bulk modulus, shear modulus, and Young’s modulus are evaluated by Voigt-Reuss-Hill approximations. All these elastic moduli exhibit a monotonic feature as a function of pressure. The Poisson’s ratio, and Pugh’s criterion indicate that the ductility of this quaternary Ba3GeTeS4 compound is more and more prominent with increasing applied pressure. Meanwhile, the analysis of the electronic structures reveals that the states near the valence band top are derived from Te 5p, S 3p, and Ba 6 s orbitals, and the lowest conduction band is composed of Ge 4 s and S 3p orbitals. We expect that the findings predicted the physical properties of this compound will promote future experimental studies on Ba3GeTeS4.

Investigation of high-pressure effect on the physical properties of FrNBr3 (N[dbnd]Ca, Sr) non-toxic halide perovskites

Utilizing ab-initio modeling, this study analyzes the possibility of replacing Lead with Francium halide perovskite for use in potential photovoltaic or optoelectronic device applications. Density functional theory is employed to estimate the structural, electronic, bonding, optical, anisotropic elastic, and mechanical characteristics of FrNBr3 (NCa, Sr) at various hydrostatic stresses scaling from 0 to 80 GPa. The calculation of the tolerance factor validates the structural stability. At 0 GPa pressure, the computed lattice constants for FrCaBr3 and FrSrBr3 are 5.78 Å (5.38 Å) and 6.03 Å (5.62 Å), respectively, using GGA (HSE03) approximation potential. FrNBr3 (NCa, Sr) perovskites show increased band gap values using the HSE03 method. Notably, these HSE03-derived values align with the trends observed in the GGA-PBE scheme, under both normal and hydrostatic pressure conditions. As pressure increases, both the lattice constant and unit cell volume decrease significantly. The estimated direct band gaps demonstrate the semiconducting nature of the compounds under ambient pressure. However, when pressure increases, the band gap narrows, increasing conductivity, and makes it as one of the great contenders of microelectronics as well as tandem photovoltaics due to its shift from ultraviolet to visible light energy region. Applying pressure enhances the optical properties, showcasing its utility in various semiconductor applications within the visible ranges and overcoming its limited usage in the ultraviolet domain. In the same vein, the application of hydrostatic pressure significantly impacts mechanical properties without compromising stability. The ductile and anisotropy character become more pronounced when pressure is exerted.

Investigating the electronic structure, elastic, magnetic, and thermoelectric nature of NiV X Sc1−X Sb quaternary half-Heusler alloys

The structural, electronic, magnetic, elastic, and thermoelectric properties of NiV x Sc1−x Sb half Heusler alloys with different compositions were investigated employing a self-consistent first-principles-based calculation that uses the full-potential linearized-augmented-plane-wave method. The structural characteristics, such as the bulk modulus and lattice constants, are examined with various vanadium concentrations. The accurately modified Becke Johnson potential was used to calculate the band gap energies. The equilibrium lattice parameter of the NiScSb type-I structure has the lowest energy and seems to be most stable among the other configurations, with a lattice constant value of 6.04 Å, which deviates from the experimental results by up to 0.5%. The bulk modulus rises as the lattice constant decreases. The ground states of the studied alloy structures are dynamically stable, as concluded by the non-existence of negative phonon frequencies. The band structure of NiScSb (for x = 0) was predicted as a non-magnetic semiconductor with an indirect band nature and an energy gap value of 0.244 eV along (Γ-point > X). This tendency was further supported by the symmetrical shape of the curves that reflect the densities of states for these configuration channels. The thermoelectric characteristics of these various combinations were also thoroughly investigated and discussed.

Infrared spectra and electronic structural changes of DNTF under high pressure: experimental and theoretical studies.

3,4-Bis(3-nitrofurazan-4-yl)furoxan (DNTF) is a novel energetic material with an excellent performance and has attracted considerable attention. Motivated by recent theories and experiments, we had carried out experimental and theoretical studies on the high-pressure responses of vibrational characteristics, in conjunction with structural and electronic characteristics. It is found that all observed infrared spectra peaks seem to shift towards higher frequencies. And the peaks attributed to N-Oc (coordinated oxygen atom) stretching vibrations become broader due to the decrease of lattice constants and the free region of DNTF crystals with the increase of pressure, where the a-direction is more sensitive to pressure. In addition, the non-covalent interaction between adjacent DNTF molecules in the same layer changes from the van der Waals interaction to the steric effect with the increase of pressure, and that between layers also changes from the van der Waals interaction to the π-π stacking interaction. More importantly, these results highlight that the increase of pressure may lead to the stability decrease and impact the sensitivity increase of DNTF. This study can deepen the understanding of the energetic material DNTF under high pressure and is of great significance for blasting and detonation applications of DNTF.

Phase Transition Engineering of Vanadium Dioxide Induced by Oxygen Vacancies

A reconfigurable optical functional system is a pioneering and comprehensive approach for portable future flexible electronics, irrespective of traditional silicon-based technology. VO2 shows tremendous temperature-dependent structural and electrical phase transitions as a complex correlated metal oxide, presenting it as a potential candidate for bolometers, thermal camouflage, and optoelectronics applications. However, the structural stability and high transition temperature restrict room-temperature applications. The present study reports the oxygen vacancies-assisted phase transition engineering in the VO2/muscovite heterostructure. The ion bombardment alters the oxygen stoichiometry of VO2/muscovite thin film at room temperature. A significant decrease in lattice constant has been observed during the transition of the insulating M1 (monoclinic) phase into the metallic R (tetragonal) phase, which was confirmed through high-resolution XRD. The change in oxygen vacancy concentration determined using X-ray photoelectron spectroscopy (XPS) actively suppressed and stabilized the epitaxial thin film of VO2 near room temperature. We investigated whether applying increasing power-mediated ion bombardment for a few minutes affects the oxygen vacancy formation on the VO2/muscovite film’s surface. Consequently, a change in KPFM and 4 orders of magnitude change in resistance of VO2 thin film have been observed. This report reveals the fundamental understanding of controlling the MIT in epitaxial VO2 thin film via facile and clean phase transition engineering techniques for advanced flexible electronic devices.

Structural, electronic, optical, and thermoelectric properties of CsPbI3-yBry (y = 0.5, 1.5, 2.5) compounds: First-principle study

BackgroundAmong photovoltaic materials, halide-based perovskites, such as CsPbI3, have been the subject of many research papers due to their suitable and direct bandgap, very good optical properties, and remarkable thermoelectric properties. Enhancing optoelectronic and thermoelectric properties can be achieved by combining halide atoms intelligently. The purpose of this article is to examine the physical properties of Br substitution at different concentrations in CsPbI3 perovskite. MethodsThe structural, electrical, and optical properties of CsPbI3-yBry (y = 0.5, 1.5, 2.5) compounds have been investigated by using the QUANTUM-ESPRESSO/PWSCF computational package which is based on the density functional theory and the pseudo-potential technique. The thermoelectric properties of CsPbI3-yBry perovskites were calculated by solving the Boltzmann transport equations within the constant relaxation time approximation as employed in the BoltzTraP package. Significant findingsThe structural investigation reveals that when the I atom is substituted by Br, the lattice constant decreases, increasing the bulk modulus and stiffness of compounds. The calculated negative formation energy confirmed the thermodynamic stability of CsPbI3-yBry compounds, and the stability improved with an increase in Br concentration. The electronic investigation indicates the semiconductor nature of compounds with a direct band gap, with a slight increase in electronic band gap as Br concentration increases. The noticeable optical absorption coefficient in the visible range of the electromagnetic spectrum, along with high and tunable optical conductivity, confirms the capability of the compounds for use in optoelectronic devices. The positive value of the Seebeck coefficient revealed the p-type semiconducting nature of CsPbI3-yBry perovskites. Lattice thermal conductivity calculation reveals that this quantity is decreased because of the increase in phonon-phonon interaction due to rising temperature. Thermoelectric investigation indicates that a precise mixture of halide I and Br atoms significantly enhances the electrical and thermal conductivity of perovskites. Also, the substitution of halide I atoms by Br can improve the figure of merit (ZT). The maximum value of ZT at room temperature is equal to 0.99, justifying the brilliant thermoelectric properties of the studied compounds.

Temperature dependent magnetic and electrical transport properties of lanthanum and samarium substituted nanocrystalline nickel ferrite and their hyperthermia applications

Structural, optical, temperature dependent magnetic and electrical properties have been investigated for the nanocrystalline NiFe1.97RE0.03O4 (RE = La3+ and Sm3+) compound. Without any signs of a secondary REFeO3 phase, the Rietveld refinement reveals a single-phase spinel structure possessing cubic symmetry for current samples. The decrease in lattice constant has been observed as a result of RE ions substitution. The TEM micrographs reveal nanosized particles with an average size of 35 ± 3 nm and 32 ± 3 nm for La3+ and Sm3+ substituted samples. EDX spectra of both samples show good compositional homogeneity. HRTEM micrographs of both samples show well resolved lattice fringes and their inter-planar spacing matches with that obtained from the Rietveld analysis of the XRD patterns. The concentration of Fe2+ and Fe3+ ions has been estimated from the XPS spectra analysis and it is found to be ∼ 22% and 78% for NiFe1.97La0.03O4 and, 20% and 80% for NiFe1.97Sm0.03O4 compound. The optical energy band gap for rare earth substituted samples is found to be more than that of pure nickel ferrite. The value of saturation magnetization (Ms) and magneto-crystalline anisotropy constant (K1) estimated from the “Law of Approach to Saturation” equation for rare earth substituted samples are found to be less than that of pure nickel ferrite. However, an enhanced value of coercivity has been observed with RE substitution. ZFC (zero field cooling) and FC (field cooling) DC magnetization curves measured at 100 Oe in the temperature range of 60–400 K reveal a combination of weak and intermediate forms of magnetic interaction between the particles for both samples. Temperature dependent analysis of saturation magnetization and coercivity employing modified Bloch’s law and Kneller’s relation supports the nanomagnetic behavior of both samples. Under an AC magnetic field of 14.92 kA/m and frequency 337 kHz, the SAR and ILP values have been found to be ∼ 331 W/g and 4.22 nHm2/kg for NiFe1.97La0.03O4 and, ∼ 241 W/g and 3.21 nHm2/kg for NiFe1.97Sm0.03O4. The dielectric relaxation data have been analyzed at various temperatures ranging from 40 to 300 0C over the frequency range 100 Hz-1 MHz using electrical impedance spectroscopy. The dielectric constant for rare earth substituted samples is found to be more and their AC conductivity is observed to be less than that of pure nickel ferrite. The analysis of temperature dependent AC conductivity employing Jonscher’s power law suggests that the charge carrier’s conduction mechanism of both samples follows the small polaron hopping mechanism below 200 0C, thereafter; it follows the correlated barrier hopping mechanism. The activation energy estimated by imaginary impedance spectra is found to be 0.411 eV and 0.398 eV for NiFe1.97La0.03O4 and NiFe1.97Sm0.03O4 which is more than that of pure nickel ferrite. The Cole-Cole plots at different temperatures suggest the presence of non-Debye-type relaxation. The modeling of Cole-Cole plots with equivalent circuits for both samples confirms the contribution of both grain and grain boundary in electrical conduction. The estimated stretching exponential factor by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary modulus curve reveals relatively more dipole-dipole interaction in NiFe1.97Sm0.03O4 than that of the La3+ substituted sample.

Novel investigation by TB-mBJ potential of magneto-electronic properties and magnetic exchange coupling in vanadium (V)-doped PbTiO3 perovskite oxide

ABSTRACT In this paper, we investigated the structural and magneto-electronic properties, and exchange coupling in new vanadium (V)-doped PbTiO3 perovskite oxide such as PbTi1−xVxO3 compounds with compositions of x = 0, 0.25, 0.5, 0.75, and 1. The calculations of these properties are based on density functional theory using the generalized gradient approximation of Wu-Cohen (GGA-WC) and the Tran-Blaha-modified Becke–Johnson potential (TB-mBJ). Our calculations with GGA-WC revealed that the lattice constant for PbTiO3 is in good concordance with other theoretical and experimental results, while for PbTi1−xVxO3 at x = 0.25, 0.5, 0.75, and 1, the lattice constant decreases with increasing vanadium concentration owing to the difference in sizes of Ti and V ionic radii. The improved electronic structures obtained by employing the TB-mBJ potential, demonstrated that the half-metallic ferromagnetic and half-metallic gaps are present in PbTi1−xVxO3 materials at x = 0.25, 0.5, 0.75, and 1, which makes them promising candidate materials for spintronics applications.