Lattice Constant Decreases Research Articles

Revealing Grain Boundaries and Defect Formation in Nanocrystal Superlattices by Nanodiffraction.

X-ray nanodiffraction is applied to study the formation and correlation of domain boundaries in mesocrystalline superlattices of PbS nanocrystals with face-centered cubic structure. Each domain of the superlattice can be described with one of two mesocrystalline polymorphs with different orientational orders. Close to a grain boundary, the lattice constant decreases and the superlattice undergoes an out-of-plane rotation, while the orientation of the nanocrystals with respect to the superlattice remains unchanged. These findings are explained with the release of stress on the expense of specific nanocrystal-substrate interactions. The fact that correlations between adjacent nanocrystals are found to survive the structural changes at most grain boundaries implies that the key to nanocrystal superlattices with macroscopic domain sizes are strengthened interactions with the substrate.

Structural, electronic and optical properties of cubic perovskite RbYbF3 under pressure: a first principles study

We report the ground state and pressure induced structural, electronic and optical properties of RbYbF3 calculated via density functional theory implemented in the Wien2k code. The ground state lattice parameters were found in good agreement with the available experimental and theoretical results. To evaluate the pressure induced effects on RbYbF3, stepwise pressure in the range of 0–15 GPa was virtually imposed with each step of 3 GPa. It was noted that the lattice constant and bond length decrease with increase in pressure, however, the cubic structure of RbYbF3 remains unchanged. The band structure calculation shows a direct band gap of 0.80 eV that gradually decreases to 0.62 eV at 15 GPa pressure. The optical properties calculated within energy range 0–13.5 eV show that all the optical parameters shifts towards higher energies under the influence of pressure. The direct band gap nature and higher absorption capability of RbYbF3 in ultraviolet and visible range of electromagnetic spectrum indicates that it can be efficiently used in optoelectronic devices working in these range.

Calculations of the structural and optoelectronic properties of cubic CdxZn1−xSeyTe1−y semiconductor quaternary alloys using the DFT-based FP-LAPW approach

The structural and optoelectronic properties of technologically important CdxZn1−xSeyTe1−y quaternary alloys have been calculated using the density functional theory (DFT)-based full potential (FP)-linearized augmented plane wave (LAPW) approach. The exchange–correlation potentials are calculated using the Perdew–Burke–Ernzerhof (PBE)-generalized gradient approximation (GGA) scheme for the structural properties and both the modified Becke–Johnson (mBJ) and Engel–Vosko (EV)-GGA schemes for the optoelectronic properties. A direct bandgap ($$ \varGamma $$–$$ \varGamma $$) is observed for all the examined compositions in the CdxZn1−xSeyTe1−y quaternary system. At each cationic (Cd) concentration x, the lattice constant decreases while the bulk modulus and bandgap increase nonlinearly with increasing anionic (Se) concentration y. On the other hand, a nonlinear increase in the lattice constant but a decrease in the bulk modulus and bandgap are observed with increasing cationic concentration x at each anionic concentration y. The contour maps calculated for the lattice constant and energy bandgap will be useful for designing new quaternary alloys with desired optoelectronic properties. Several interesting features are observed based on the study of the optical properties of the alloys. The compositional dependence of each calculated zero-frequency limit shows the opposite trend, while each calculated critical point shows a similar trend, with respect to that found for the compositional dependence of the bandgap. Finally, the results of these calculations suggest that ZnTe, InAs, GaSb, and InP are suitable substrates for the growth of several zincblende CdxZn1−xSeyTe1−y quaternary alloys.

Presence of neodymium and gadolinium in cobalt ferrite lattice: Structural, magnetic and microwave features for electromagnetic wave absorbing

In this work, neodymium substituted gadolinium-cobalt ferrite nanoparticles were synthesized by hydrothermal method. The significant role of doping both the Nd3+ and Gd3+ ions to cobalt ferrite in manipulating the cation distribution and further in influencing structural and magnetic properties was experimentally studied and reported. The influence of Nd3+ substitution was investigated with step of 0.02–0.1 into the optimized Gd-Co compound. The crystal structure formation and crystallite size were explored by X-ray diffraction analysis in which the crystallite size and lattice constant decrease with increasing the Nd3+ substitution. The microstructural properties were studied by field emission scanning electron microscopy and atomic force microscopy studies. The obtained structural and morphological results reveal that the substitution of Nd3+ with more than 0.06 into the Gd-Co ferrites will change the material behavior and trends. The saturation magnetization and coercivity values were measured using a vibration sample magnetometer at room temperature. Comparative microwave absorption experiments demonstrate that the reflection loss properties enhance with increasing substitution of Nd3+ cations in Gd-Co ferrite spinel structure. This research reports that the as-prepared Nd3+ substituted Gd-Co ferrite compound stands as promising candidate for absorbing electromagnetic wave with a wider absorbing bandwidth of X-band.

Structural, morphological and magnetic properties of Ni–Co ferrites by the Mn2+ ions substitution

Manganese substituted nickel–cobalt ferrite nanoparticles having the basic composition Ni0.2MnxCo0.8−xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4) were synthesized using sol–gel auto combustion method. The effect of Mn substitution on structural and magnetic properties of nickel–cobalt ferrite has been studied. All the prepared samples show that the single-phase cubic spinel structure by X-ray diffraction. The average microcrystalline size of the prepared samples is about 50 nm calculated by Scherrer equation. With the increase of Mn content, the lattice constant decreases first and then increases for the prepared samples. Fourier transform infrared measurements also confirm the formation of the cubic spinel structure of ferrite. The absorption peak of the Fe–O bond at tetrahedral position shifted to the low frequency with the increase of manganese ion content. By transmission electron microscope observation of the preparation of samples with spherical cube crystallite particles. Energy dispersive X-ray confirmed that the synthesis with pure phase and structure of ferrite, and successfully realized the Mn2+ doping. Vibration sample magnetometer measurement confirm that the Ni0.2MnxCo0.8−xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4) nanoparticles have ferromagnetic behavior. It is observed that the saturation magnetization (Ms), remanent magnetization (Mr), rectangular ratio (Mr/Ms) and magnetic moment are decreasing with the increase of manganese ion content. The prepared ferrites have high coercivity, and the decrease of coercivity of samples is due to excessive Mn substitution. At the same time, the magnetization is expected to decrease because of the conversion of equivalent amounts of Fe3+ (5 µB) to Fe2+ (4 µB).

Defects characterisation and studies of structural properties of sol–gel synthesised MgFe2O4 nanocrystals through positron annihilation and supportive spectroscopic methods

ABSTRACTMagnesium ferrite (MgFe2O4) nanocrystalline samples were prepared by sol–gel method and by sintering at temperatures from 300°C to 1000°C. X-ray diffraction and electron microscopic studies showed an increase in crystallite sizes and a decrease in lattice constants at higher sintering temperatures. UV-Vis absorption measurements depicted blue shift for samples of smaller crystallite sizes (dc) with a resultant increase of the band gap energies (Eg. = 2.07 eV at dc = 49 nm to 3.10 eV at dc = 6 nm, for samples sintered at 1000°C and 300°C, respectively). Fourier transform infrared spectroscopy of the samples proved the formation of the spinel structure while energy dispersive X-ray analysis pointed out the non-stoichiometric composition, which implied the presence of vacancy type defects that could modify the structural and magnetic characteristics of the compounds. This necessitated the use of positron annihilation lifetime and coincidence Doppler broadening spectroscopic studies for defect characterisation and the results indicated distinct redistribution of cations within the unit cells, making the compound overwhelmingly turn towards a normal spinel configuration at smaller nanocrystalline sizes. Positrons were trapped in larger vacancies of increasing numbers in smaller crystallites. The vacancies turned out to be formed at the octahedral sites where the increased ionic radius of Fe3+ became large enough to reduce the occupancy significantly. Mossbauer spectra analysis indicated an increase of the ferromagnetic properties in samples sintered at higher temperatures. At 300°C and 400°C, the samples dominantly showed paramagnetic behaviour.

Crystallographic and Magnetic Properties of Double Perovskite Oxide Ba2−xSrxFeMoO6

In order to study on the change of magnetic properties according to the tolerance factor, polycrystalline single phase double perovskite oxide Ba2−x;SrxFeMoO6 (x = 0.0, 0.5, 1.0, 1.5, 2.0) are prepared. The crystallographic and magnetic properties have been studied by X-ray diffraction, magnetization measurements and Mossbauer spectroscopy. The Ba2FeMoO6 is analyzed as a cubic structure with Fe3+ and Mo5+ ions ordered at the B-sites. As the x value increases from the cubic structure, the lattice constant decreases more rapidly in the a-b-axis direction than in the c-axis. So that the tetragonal structure starts from x = 1.0. The Curie temperature of the Ba2FeMoO6 and Sr2FeMoO6 were 345 K and 425 K, respectively. As the value of x increases, the Curie temperature increases linearly. In addition, the magnetic hyperfine field fluctuation due to relaxation effects are observed in the Mossbauer spectrum of all series samples.

Comparative Studies on Structural Properties and Total Energetics of Nonequivalent Hexagonal Polytypes for a Wide Variety of Metallic Systems

Since the functionalities of materials usually originate from the spatial inhomogeneity in the associated systems, the local inhomogeneity such as defect, surface, interface, and nanostructure often assumes an important role for developing sophisticated materials. In this paper, among the many phenomena related to inhomogeneity in materials, we will report our computational research on the phenomenon called "Polytypism". Polytypism is a special case of polymorphism when the two polymorphs differ only in the stacking of identical two-dimensional sheets or layers. The polytypes are characterized by a stacking sequence with a given repeating unit along a directional axis (c-axis) and are theoretically possible to have endless permutations of the sequences. Among these polytypes, the crystalline systems composed of close-packed (CP) layers have especially attracted attention on their fundamental and technological properties for many years. While these polytypes are often experimentally observed in wide-bandgap semiconductors, SiC is particularly known to show several hundred polytypes [1]. In addition, the long period stacking ordered (LPSO) Mg alloys with light weight, high specific strength, and high heat resistance are also recently drawing attention as a metallic system with similar polytypism to that in SiC [2]. We have proposed a computational method coupled with three theoretical tools (PGA: polytype generation algorithm; FPC-DFT: first-principles calculations based on the density functional theory; and ANNNI: axial next-nearest-neighbor Ising model), which can make us possible to efficiently investigate the structural energetics for diverse nonequivalent polytypes [1]. In the present study, also motivated by the recent research activities on the LPSO [2], we have systematically evaluated the static energetics of metallic polytypes for a wide variety of elements based on the same computational method proposed by the authors [1]. For all these elemental systems, the atomistic geometry, energetics, and electronic structure for all polytypes with up to the periodic stacking length of L=13 (165 kinds of polytypes in total) have been carefully calculated based on the DFT within the GGA. Using the ANNNI model extracted from the GGA calculations, some trends of physical properties will be illustrated for the tremendous kinds of nonequivalent stacking polytypes based on the efficient PGA. In the CP structures, three different layers are often denoted by A, B, and C, corresponding to different atomistic positions in the planes perpendicular to the stacking direction (c-axis). These descriptions for nearest neighbor stacking result in the so called “hk” notation, where a letter “h” is assigned to each layer with the same type of layer at both sides (e.g., AXA, BXB, CXC) and a letter “k” is assigned otherwise. Using this “hk” notation, the “hexagonality”(σH ) is essentially defined as σH=nh/(nh+nk), where nh and nk are numbers of layers in a hexagonal or cubic environment, respectively [1]. Figure 1 exemplifies the increments of (a) lattice constants in the basal plane (a-axis) and (b) total energies as a function of hexagonality for the nonequivalent polytypes composed of Be, Mg, Pd, and Pt within the present GGA calculations. The figure implies that both physical values are depicted based on those in the 3C (fcc) configuration. We have found that these values have a strong linear correlation with hexagonality in the polytypes for any elemental systems except for La with 4H ground state. The rate of change of both physical values with respect to hexagonality in Mg is found to be significantly smaller than those in other elemental systems. Therefore, the trend should be key factors for the formation of stacking faults, twin boundaries, and also LPSO structures experimentally observed in Mg-based alloys [2]. Focusing on Fig.1 (a), it should be noticed that the a-axis lattice constant decreases with increasing hexagonality in the elemental systems with 3C (fcc) ground state and the opposite trend is true in the systems with 2H (hcp) ground state. Kaneko et al. have experimentally reported that the property of oxygen reduction reaction (ORR) on the catalytic Pt surface is maximized with a 2.0% surface compression strain [3]. Since the compression ratio of lattice constant against hexagonality can be reached around 1.5% in Pt system, the ORR performance may be sufficiently influenced by the stacking faults and/or twin boundaries in the vicinity of surface. Therefore, control of the polytypism in metallic systems may provide interesting functionalities of materials in various fields of solid-state science. [1] K. Moriguchi, et al., J. Mater. Res. 28, 7 (2013) and references therein.[2] E. Abe et al., Phil. Mag. Lett, 91, 690 (2011). [3] S. Kaneko et al., J. Phys. Chem. Lett, 8, 5360 (2017). Figure 1

Investigation on samarium and yttrium co-doping barium zirconate proton conductors for protonic ceramic fuel cells

Abstract Trivalent rare-earth cation (R 3+ ) and Y 3+ co-doped BaCeO 3 materials show an enhanced proton conductivity than single Y doped BaCeO 3 material. For the same purpose, Sm 3+ and Y 3+ as paired ions are incorporated into BaZrO 3 perovskite structure. The crystal structure, electrical conductivity and sinterability of Sm 3+ and Y 3+ co-doped BaZr 0.8 Y 0.2-x Sm x O 3-δ (BZYS, x = 0, 0.05, 0.1, 0.15, 0.2) materials are investigated for the potential electrolyte application of protonic ceramic fuel cells. Powder XRD diffraction shows BZYS with the cubic perovskite structure and a decrease of lattice constants with increasing Sm 3+ content indicates Sm 3+ doped into perovskite B site. Although the sinterability enhances by Sm 3+ introduction, the grain interior conductivity, specific grain boundary conductivity and total conductivity all cannot be improved. This proves that, unlike BaCeO 3 proton conductors, Sm 3+ and Y 3+ co-doping strategy cannot improve the charge transport properties of BaZrO 3 proton conductors, which is the main contribution of this paper. Through comprehensively considering sinterability and electrical conductivity, the BZYS5 (BaZr 0.8 Y 0.15 Sm 0.05 O 3-δ ) is considered as the potential electrolyte material and the corresponding protonic ceramic fuel cell shows the peak power density of 180 mW cm −2 at 700 °C.

Influence of Cr3+ substitution on structural, morphological, optical, and magnetic properties of nickel ferrite thin films

The NiFe2−xCrxO4 (0.0 ≤ x ≤ 1.0 in the step of x = 0.2) thin films have been synthesized using chemical spray deposition technique. The effects of Cr3+ content on the structural, morphological, optical and magnetic properties of these thin films have been investigated. The X-ray diffraction patterns confirmed single phase cubic spinel structure with space group of Fd-3m. The lattice constant decreases with increases Cr3+ concentration obeying Vegard’s law. The functional studied of Cr3+ substitution NiFe2O4 thin films were formed two major transmission bands, high-frequency band (ν1) around at 665 cm−1 is due to intrinsic vibrations of (A) site and the low frequency band (ν2) around 428 cm−1 is due to [B] site, respectively. Surface morphology was investigated in terms of root mean square roughness, average roughness (Ra), surface kurtosis and surface skewness of Ni–Cr ferrite thin films. The energy band gap for allowed direct electronic transition found to be in the range of 2.75–3.02 eV with Cr3+ content. According to VSM results show that, the saturation magnetizations of the thin film samples were found to be in the range of 234.12–46.65 emu/cc. The Cr3+ concentration increases with a reduction in hysteresis losses as well as slight reduction in the saturation magnetization.

Facile synthesis and ferrimagnetic property of spinel (CoCrFeMnNi)3O4 high-entropy oxide nanocrystalline powder

(CoCrFeMnNi)3O4 high-entropy oxide nanocrystalline powder with chemical and microstructure homogeneity has been successfully synthesized, for the first time by a modified solution combustion synthesis method at synthesis temperature above 623 K. The XRD patterns with Rietveld refinement reveal the formation of spinel crystal structure with Fd-3m space group. The crystallite size increases from 5.3 to 43.8 nm, the lattice constant decreases from 8.354 to 8.287 Å, whereas the lattice distortion initially decreases and then increases slightly with the increase of synthesis temperature. Magnetic studies indicate all synthesized nanocrystalline powders exhibit a typical ferrimagnetic behavior at room temperature. The values of saturation magnetization and coercivity of synthesized (CoCrFeMnNi)3O4 are in the range of 4.85–15.98 emu/g and 176.55-21.39 Oe, respectively. Crystallinity, crystalline size, lattice constant and lattice distortion are the determining factors of how the microstructure will get controllable, and results in variations of magnetic properties.

Magnetic and transport properties of Zr1−xNbxCo2Sn

ZrCo2Sn is a potential candidate as a Weyl semimetal with a ferromagnetic ground state, and Nb-doping is expected to shift the Weyl points to the vicinity of Fermi level. We successfully synthesized a series of Zr1−xNbxCo2Sn single crystals with various concentrations of Nb (x = 0, 0.1, 0.2, 0.275, 0.4, 0.5). All samples have a spinel structure and the lattice constant decrease as the Nb doping level increases. The magnetization and transport measurements suggest that the ferromagnetic ordering temperature can be strongly modified by the Nb doping. When x increases, the Curie temperature decreases significantly, accompanied by a change from metal-like to semiconductor-like behavior. There is a crossover for positive to negative MR at a temperature between 30 K to 50 K. In constant, the magnitude of the anomalous Hall resistance increases monotonously with decreasing temperature.

Theoretical characterization of C doped SiGe monolayer

Two dimensional Si1−xGeCx (SGC) alloys have been investigated within the framework of density functional theory using the hybrid functional of Heyd-Scuseria-Ernzerhof for the electron exchange correlation potential. The site occupancy disorder program is used to predict the most stable configuration for different values of carbon (C) concentration (x). With increasing C content, the lattice constant decreases almost linearly, while there is a reversal in the bandgap bowing for x>0.50. Besides the ideal solid solutions, we have also studied the effect of the C dimer. The calculated mixing enthalpy suggests that the growth of the alloys follows the endothermic reaction. The spinodal and binodal decomposition curves for Si and C rich phases have been explained along with a growth temperature equal to 2675 K. The valence and conduction band edges are aligned with respect to the vacuum level. The calculated optical absorption coefficient of SGC alloys is greater than 104cm−1, suggesting that these alloys are promising materials for opto-electronic applications. Our results may motivate experimentalists to synthesize these alloys which show promise for efficient thin film devices.

Effect of Cr3+ Substitution on the Structural, Electrical and Magnetic Properties of Ni0.7Zn0.2Cu0.1Fe2−xCrxO4 Ferrites

In this work, Ni0.7Zn0.2Cu0.1Fe2−xCrxO4 (x = 0.02, 0.04, 0.06, 0.08 and 0.1) ferrites were synthesized by using the solid state reaction method and how relevant properties of the samples were modified accordingly. The structural, morphological, magnetic and electrical features of the ferrites were evaluated by using X-ray diffraction, scanning electron microscopy, Fourier transmission infrared (FTIR) spectra, vibrating sample magnetometry, electron spin resonance and network analyser. The lattice constant decreases with increasing chromium concentration and the decrease in the lattice constant is attributed to the ionic radius of chromium being smaller than that of iron. The distribution of metal cations in the spinel structure was estimated from the X-ray diffraction data and showed that along with Ni2+ ions, most of the Zn2+ and the Cu2+ ions additionally occupied the octahedral [B] sites. The FTIR spectra revealed two prominent frequency bands in the wave number range 400–600 cm−1 which confirm the cubic spinel structure. The magnetic properties, such as the initial permeability, saturation magnetization and coercivity, were investigated at room temperature. The frequency-dependent dielectric constant was observed to decrease with increasing chromium concentration. This behavior was using Koops phenomenological theory.

Structural, elastic and optoelectronic characteristics of BexZn1−xS, BexZn1−xSe and BexZn1−xTe alloys-a density functional based FP-LAPW study

Structural, elastic and optoelectronic features of BexZn1−xS, BexZn1−xSe and BexZn1−xTe alloys are computed employing DFT based FP-LAPW approach. Structural features with WC-GGA functional show that lattice constant decrease and bulk modulus increase nonlinearly with increase in Be-concentration in each alloy system. The elastic constants C11andC44for cubic specimens increase, whileC12decrease with increase in Be-concentration in each system. Elastically anisotropic specimens at x = 0.0 and 0.25 are ductile, while at x = 0.50, 0.75 and 1.0 are brittle in nature. The electronic properties, computed with mBJ, EV-GGA and PBE-GGA functional, predict each ternary sample as a direct band gap (Γ-Γ) semiconductor. Band gap increases nonlinearly with Be-concentration in each system. Chemical bonding between beryllium and chalcogen are ionic and between zinc and chalcogen are covalent in nature. In optical transitions, chalcogen-p in valence band as initial states and Be-3s, 2p as well as Zn-5s states in conduction band as final states play the leading role. Nature of variation of each of theε1(0), n(0)and R(0)with Be-concentration x is opposite, while critical point in each of the ε2(ω)k(ω),σ(ω) and α(ω) spectra with Be-concentration x is similar to the nature of variation of band gap with Be-concentration in each alloy system.

Density functional study of structural, elastic, electronic and optical properties of BexCd1−xS, BexCd1−xSe and BexCd1−xTe alloys using FP-LAPW approach

Structural, elastic, electronic and optical features of cadmium-beryllium-chalcogenide ternary alloys BexCd1−xS, BexCd1−xSe and BexCd1−xTe have been computed employing density functional theory (DFT) based FP-LAPW approach. Structural features have been computed with Wu-Cohen (WC)-GGA functional and found that the lattice constant decreases, while bulk modulus increases nonlinearly with Be-concentration in each alloy system. Each of the elastic constants C11, C12 and C44 for the cubic specimens in each alloy system increases with in Be-concentration. Moreover, each specimen shows elastic anisotropy. Specimens at x = 0.0 and 0.25 are found to be ductile in nature, while those at x = 0.50, 0.75 and 1.0 show brittle nature. The electronic properties are explored with the modified Becke-Johnson (mBJ), Engel-Vosko (EV)-GGA and Perdew-Burke-Ernzerhof (PBE)-GGA functional and found that each ternary sample is a direct band gap (Γ-Γ) semiconductor. Band gap for each alloy system increases nonlinearly with Be-concentration. Chemical bonding between beryllium and chalcogen are ionic and that between cadmium and chalcogen are covalent in nature. In case of optical transitions, the chalcogen-p of valence band as initial states and Be-3s, 2p as well as Cd-6s states of conduction band as final states play the dominant role. In each alloy system, nature of variation of each of the static dielectric constant, static refractive index and static reflectivity with Be-concentration x is opposite, while critical point in each of the ε2(ω), k(ω), σ(ω) and α(ω) spectra with Be-concentration x is similar to the nature of variation of band gap with Be-concentration. Several calculated properties are found to agree well with the corresponding experimental findings.

Structural and magnetic properties of La3+ ion doped Ni–Cu–Co nano ferrites prepared by sol–gel auto-combustion method

Lanthanum doped Ni–Cu–Co nano ferrites with the chemical composition Ni0.2Cu0.1Co0.7Fe2−xLaxO4 (x = 0.0, 0.025, 0.05, 0.075, 0.1) were prepared by sol–gel auto-combustion technology. All samples were sintered at a temperature of 950 ℃. The X-ray diffraction (XRD) analysis verifies that all the samples of the formation of the cubic spinel structure. It turns out that with the addition of La3+ ions, the lattice constant decreases, and with the addition of La3+ ions, the lattice constant increases. The obtained Fourier transform infrared (FT-IR) measurement also confirms the formation of the spinel structure. With the increase in La, the higher frequency ν1 is slightly moving toward the high-frequency side. Transmission electron microscopy (TEM) images show the presence of particles, which are spherically cubic shaped crystallites. The presence of constituent’s, i.e., the presence of ingredients, namely, Ni, Cu, Co, Fe and La were authenticated by energy dispersive X-ray analysis (EDX). It was confirmed La3+-doping was successfully achieved. The magnetic parameters were measured by Vibrating sample magnetometer (VSM). The saturation magnetization, remanent magnetization, coercivity, anisotropy constant first increase and then decrease with the La content increases. The sample had the best magnetic properties when the doping content of La at x = 0.025. This indicates that appropriate doping can improve the magnetic properties of the samples. The reduction of the magnetic moment can be attributed to non-magnetic La3+ ions in place of Fe3+ ions (5µB), which results in a reduction of net total magnetic moment.

Microstructure, Enhanced Relaxor-Like Behavior and Electric Properties of (Ba0.85Ca0.15)(Zr0.1−xHfxTi0.9)O3 Ceramics

(Ba0.85Ca0.15)(Zr0.1−xHfxTi0.9)O3 (BCZHT) ceramics were fabricated by a conventional solid-state reaction method. The effects of Hf4+ on microstructure and electric properties of BCZHT ceramics have been systematically investigated. The x-ray diffraction (XRD) results indicate that the introduction of Hf4+ in BCZHT ceramics induces phase transition from an orthorhombic phase to the coexistence of tetragonal and orthorhombic phases, and the lattice constant decreases with the increasing of Hf4+ content caused by substitution of Hf4+ for Zr4+ at B sites. As Hf4+ content increases, the densification of BCZHT ceramics is enhanced and the grain size increases. The introduction of Hf4+ at B sites results in the fall of the Curie temperature and the increase of dielectric constant in BCZHT ceramics. The temperature dependences of dielectric properties of BCZHT (x = 0, 0.05 and 0.1) ceramics show obvious diffuse phase transition characteristics, and the diffuseness of phase transition is enhanced with increasing of Hf4+ content. But there is no frequency dispersion phenomenon in BCZHT (x = 0, 0.05 and 0.1) ceramics. The substitution of Hf4+ for Zr4+ at B sites of BCZHT ceramics makes its remnant polarization increase, which results from the interaction of increased grain size and tolerance factor. When temperature is above its Curie temperature, the polarization–electric field curves of BCZHT (x = 0, 0.05 and 0.1) ceramics still show nonlinear characteristics, which further proves that there is diffuse phase transition and relaxor-like behavior. Moreover, the piezoelectric coefficient of BCZHT ceramics increases as Hf4+ content increases.

The electronic, half-metallic, and magnetic properties of Ca1-xCrxS ternary alloys: Insights from the first-principle calculations

The electronic, structural, and magnetic characteristics of Cr atom substituting Ca atom in rocksalt CaS have been investigated within the formalism of (GGA + PBE) and PBE with Hubbard correction (GGA + U). Our findings point out that the ternary alloys are dynamically stable depending on the obtained results of elastic constants. For structural properties, it is clear that the lattice constants decrease and bulk modulus increases with increasing concentration of chromium impurity. Interestingly, the perceived total magnetic moments increase with the Cr concentration and reaches the maximum for Ca0.25Cr0.75S, which is mainly composed of Cr atoms. Besides, it is found from PBE and PBE + U calculations that the Cr-substituted CaS gives half-metallic ferromagnetism (HMF). Finally, the deduced results of minority-spin bands demonstrate a half-metallic ferromagnetic gap and half-metallic (HM) gap. The predicted results confirmed that Ca1-xCrxS could be considered as a promising candidate material for spintronics applications.

Study of hydrodynamic size distribution and hyperthermia temperature of chitosan encapsulated zinc-substituted manganese nano ferrites suspension

Hyperthermia opens a safe alternative for cancer treatment. Researchers synthesize new materials that can be successfully used for the biomedical application. We have synthesized Mn1-xZnxFe2O4 (0.2 ≤ x ≤ 1.0, in the steps of 0.2) and coated the samples with chitosan. The structural properties of the nanoparticles were determined by XRD and TEM analysis. Face-centered cubic structure of the nano ferrites has been revealed by XRD analysis. It has been found that both the theoretical and experimental lattice constant decreases with the addition of zinc. The range of theoretical and experimental lattice constants is 8.336 Å to 8.275 Å and 8.460 Å to 8.399 Å, respectively. EDS studies revealed the elemental distribution of both bare and coated ferrite nanoparticles. VSM has characterized the field dependent magnetization. Mössbauer spectroscopy revealed that all samples exhibit superparamagnetic behavior except Mn0.8Zn0.2Fe2O4. The shift of iron ion in the octahedral site from the tetrahedral site was observed with the addition of zinc. The maximum hydrodynamic diameter of the coated samples was found around 220 nm which is suitable for the biomedical application. The maximum hyperthermia temperature of the coated samples has been estimated.