Hexagonal-Type Ising Nanowire with Core/Shell Structure Designed with Half-Integer Spins: Compensation Behaviors and Phase Diagrams in the Temperature and Interaction Planes

The effective field theory with correlation is used to investigate the magnetic behaviors of the mixed spin-1/2 and spin-3/2 hexagonal Ising nanowire (HIN) with core/shell in the crystal field. The total magnetization as a function of the temperature is used to describe the compensation behaviors of the system, and the N-, Q-, P-, R-, and S-type compensation types are given. The dependence of the phase diagrams on interaction parameters is studied in detail and presented the phase diagrams in the six different planes, namely (J ₁, Δ, T), (J _C, Δ, T), (J _S, Δ, T), (J ₁, J _C, T), (J ₁, J _S, T) and (J _C, J _S, T).Besides, the system exhibit second-order phase transition and first-order phase transitions, which can be found via the variations of the total magnetization with the crystal field in the mixed spin-1/2 and spin-3/2 HIN.     

Critical Current Model for Polycrystalline Compounds with an Intrinsic Solid Solution of Two Mixed Superconductor Phases

We propose an S ₁ S ₂ I S ₂ S ₁ junction model to describe the intergrain junctions of compounds with intrinsic mixtures of two superconductor phases. Considering the polycrystalline compound Hg,Re-1223 as a representative case, fitting using this model of a junction in J _c as a function of applied magnetic field μ ₀ H proves to be better than a simple SIS junction model for μ ₀ H > 1.0 mT and T≈T _C .     

Investigation of Magnetic,Magnetocaloric, and Critical Properties of La<Subscript>0.5</Subscript>Ba<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> Manganite

We present an extensive study of the magnetic properties of a novel La_0.5Ba_0.5MnO₃ perovskite material prepared by the hydrothermal method. The explored sample was structurally studied by the x-ray diffraction (XRD) method which confirms the formation of a pure cubic phase of a perovskite structure with Pm3m space group. The magnetic properties were probed by employing temperature M (T) and external magnetic field M (μ_oH) dependence of magnetization measurements. A magnetic phase transition from ferromagnetic to paramagnetic phase occurs at 339 K in this sample. The maximum magnetic entropy change (\(\left | {{\Delta } S}_{M}^{\max } \right |\)) took a value of 1.4 J kg^??1 K^??1 at the applied magnetic field of 4.0 T for the explored sample and has also been found to occur at Curie temperature (T_C). This large entropy change might be instigated from the abrupt reduction of magnetization at T_C. The magnetocaloric effect (MCE) is maximum at T_C as represented by M (μ_oH) isotherms. The relative cooling power (RCP) is 243.2 J kg^??1 at μ_oH =?4.0 T. Moreover, the critical properties near T_C have been probed from magnetic data. The critical exponents δ, β, and γ with values 3.82, 0.42, and 1.2 are close to the values predicted by the 3D Ising model. Additionally, the authenticity of the critical exponents has been confirmed by the scaling equation of state and all data fall on two separate branches, one for T < T_C and the other for T > T_C, signifying that the critical exponents obtained in this work are accurate.     

Dual relaxation behaviors and large electrostrictive properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–Sr<Subscript>0.85</Subscript>Bi<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> ceramics

Lead-free ceramics (1???x)Bi_0.5Na_0.5TiO₃–xSr_0.85Bi_0.1TiO₃ (BNT–xSBT, x?=?0.4, 0.5, 0.6 and 0.7) were prepared by a solid-state reaction process. Coexistence of ferroelectric relaxation at low temperature and Maxwell–Wagner dielectric relaxation at high temperature was revealed for the first time in this system. Meanwhile, hysteresis-free P–E loops combined with a very high piezoelectric strain coefficient (d₃₃) of 1658 pC/N concurrently with large electrostrictive coefficient Q?=?0.287 m⁴C^?2 were achieved. The ferroelectric relaxor behavior and large electrostrictive strain might be linked to easy reorientation and reversal of ergodic PNRs and the combined effect of Bi off-center position and lone pair electrons.     

X-ray Photoelectron Spectroscopy,Magnetotransport and Magnetisation Study of Nb<Subscript>2</Subscript>PdS<Subscript>5</Subscript> Superconductor

In the present report, we investigate various properties of the Nb₂PdS₅ superconductor. Scanning electron microscopy displayed slabs like laminar growth of Nb₂PdS₅ while X-ray photoelectron spectroscopy exhibited the hybridisation of sulphur (2p) with both palladium (3d) and niobium (3d). High-field (140 kOe) magneto-transport measurements revealed that superconductivity (\(T_{c}^{\text {onset}} =?7\) K and T cρ=?0 = 6.2 K) of the studied Nb₂PdS₅ material is quite robust against magnetic field with the upper critical field (H _c2) outside the Pauli paramagnetic limit. Thermally activated flux flow (TAFF) of the compound showed that resistivity curves follow Arrhenius behaviour. The activation energy for Nb₂PdS₅ is found to decrease from 15.15 meV at 10 kOe to 2.35 meV at 140 kOe. Seemingly, the single vortex pinning is dominant in low-field regions, while collective pinning is dominant in high-field region. The temperature dependence of AC susceptibility confirmed the T _c at 6 K, further varying amplitude and frequency, showed well-coupled granular nature of superconductivity. The lower critical field (H _c1) is extracted from DC magnetisation measurements at various T below T _c. It is found that H _c1(T) of Nb₂PdS₅ material seemingly follows the multiband nature of superconductivity.     

Sintering behavior,phase structure and electric properties of KNNTS-BKNZ ceramics with excessive alkali metals

We investigated the effect of excessive alkali metals on sintering character, phase structure, dielectric, piezoelectric and ferroelectric properties in KNN-based ceramics thoroughly. The 0.96(K_0.48Na_0.52)_1+xNb_0.93Sb_0.02Ta_0.05O₃–0.04Bi_0.5(K_0.12Na_0.88)_0.5ZrO₃ [(KN) _x NTS-BKNZ] lead-free piezoelectric ceramics were prepared by conventional solid-state reaction method. The sintering temperature of (KN) _x NTS-BKNZ ceramics increases gradually while the sintering temperature zone becomes narrow with the increasing x value. For the composition of x?>?0.03, the grains could not grow in all sintering temperature. The coexistence system of rhombohedral and tetragonal phases has been found in (KN) _x NTS-BKNZ ceramics and the T_R?T, T_C, d₃₃, and ε_r show a upward tendency with the increasing x when 0?≤?x?≤?0.03. The maximal piezoelectric coefficient d₃₃ of 415 pC/N was obtained at x?=?0.03. In addition, these ceramics presented good temperature stability. This study exhibits that excessive alkali metals influence sintering character and electrical properties on KNN ceramics deeply. It was believed that this work would be helpful for further understanding the effect of excessive alkali metals on sintering behavior and electric properties in KNN-based ceramics.     

High-temperature heat capacity and thermodynamic properties of Tb<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript>

Tb₂Sn₂O₇ has been prepared by solid-state reaction in air at 1473 K over a period of 200 h and its isobaric heat capacity has been studied experimentally in the range 350–1073 K. The C _p(T) data for this compound have no extrema and are well represented by the classic Maier–Kelley equation. The experimental C _p(T) data have been used to evaluate the thermodynamic properties of terbium stannate (pyrochlore structure): enthalpy increment H°(T)–H°(350 K), entropy change S°(T)–S°(350 K), and reduced Gibbs energy Ф°(Т).     

Effect of Ni Doping at Pd Site in Nb<Subscript>2</Subscript>PdS<Subscript>5</Subscript> Superconductor

The superconducting properties of Nb₂PdS₅ superconductor have been investigated with Ni doping at Pd site All the bulk polycrystalline Nb₂Pd_1?xNi_x S ₅ (0 = x ≤ 0.10) samples are crystallized in singlephase monoclinic structure. The electrical resistivity and magnetic measurements of Nb₂Pd_1?xNi_x S ₅ (0 = x ≤ 0.15) were carried out to study the variation of superconducting critical parameters with Ni doping. Superconductivity in Nb₂PdS₅ sample completely disappears for x ≥ 0.15. We observed that the ratio of upper critical field to transition temperature decreases with increasing Ni concentration. Also, the magnetization study of Nb₂Pd_1?xNi_x S ₅ (0 = x ≤ 0.15) samples shows similar superconducting behaviour. In summary, the superconductivity in Nb₂PdS₅ sample is slightly varying with partial doping of Ni at Pd site in Nb₂PdS₅ superconductor.     

Effects of Iron Contents on the Vortex State in Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>0.5</Subscript>Te<Subscript>0.5</Subscript>

We investigate the effects of iron content on the upper critical field (H _c2) and the activation energy U(T) in thermally activated flux flow in Fe _x Se_0.5Te_0.5 near the superconducting transition temperature T _c . The variations in H _c2(T) with temperature are analyzed using Ginzburg-Landau (GL), Werthamer-Helfand-Hohenberg (WHH) models along with the empirical relation (ER). The obtained values of H _c2(0) depend strongly on the model and the criteria used to determine the transition temperature. However, the general trend is that that H _c2(0) increases with the increasing Fe content. The activation energy U(T) is maximum for x =? 1 and rapidly suppressed by excess or deficiency of iron. The low values of U(T) (～10 meV) reflect the low vortex-pinning nature (due to defects, vacancies, etc.) in the Fe _x Se_0.5Te_0.5 superconductor.     

Synthesis and high-temperature heat capacity of Gd<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript>

Gd₂Sn₂O₇ gadolinium stannate with the pyrochlore structure has been prepared by solid-state reaction and its high-temperature heat capacity has been determined by differential scanning calorimetry in the temperature range 350–1020 K. The C_p(T) data are shown to be well represented by the classic Maier–Kelley equation. The experimental C_p(T) data have been used to evaluate the thermodynamic functions of gadolinium stannate: enthalpy increment H°(T)–H°(339 K), entropy change S°(T)–S°(339 K), and reduced Gibbs energy Ф°(Т).     

Effects of Ge<Superscript>4+</Superscript> acceptor dopant on sintering and electrical properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoceramics

Lead-free (K_0.5Na_0.5)(Nb_1-xGe _x )O₃ (KNN-xGe, where x = 0-0.01) piezoelectric ceramics were prepared by conventional ceramic processing. The effects of Ge⁴⁺ cation doping on the phase compositions, microstructure and electrical properties of KNN ceramics were studied. SEM images show that Ge⁴⁺ cation doping improved the sintering and promoted the grain growth of the KNN ceramics. Dielectric and ferroelectric measurements proved that Ge⁴⁺ cations substituted Nb⁵⁺ ions as acceptors, and the Curie temperature (T_C) shows an almost linear decrease with increasing the Ge⁴⁺ content. Combining this result with microstructure observations and electrical measurements, it is concluded that the optimal sintering temperature for KNN-xGe ceramics was 1020°C. Ge⁴⁺ doping less than 0.4 mol.%can improve the compositional homogeneity and piezoelectric properties of KNN ceramics. The KNN-xGe ceramics with x = 0.2% exhibited the best piezoelectric properties: piezoelectric constant d₃₃ = 120 pC/N, planar electromechanical coupling coefficient k_p = 34.7%, mechanical quality factor Q_m = 130, and tanδ = 3.6%.     

Effects of Nb doping on the microstructure,ferroelectric and piezoelectric properties of 0.7BiFeO<Subscript>3</Subscript>–0.3BaTiO<Subscript>3</Subscript> lead-free ceramics

Donor-doped lead-free Bi_0.7Ba_0.3(Fe_0.7Ti_0.3)_1?x Nb_0.66x O₃ + 1 mol% MnO₂ ceramics were prepared by a conventional oxide-mixed method and the effects of Nb-doping on microstructure, piezoelectric and ferroelectric properties of the ceramics were investigated. All the ceramics exhibit a pure perovskite structure with rhombohedral symmetry. The grain growth of the ceramics is inhibited after the addition of Nb doping. High electric insulation (R = 10⁹–10¹⁰ Ω?cm) and the poor piezoelectric performance and weak ferroelectricity are observed after the addition of Nb₂O₅ in the ceramics. Different from the donor effect of Pb-based perovskite ceramics, the introduction of Nb into 0.7BiFeO₃–0.3BaTiO₃ degrades the piezoelectricity and ferroelectricity of the ceramics. The Bi_0.7Ba_0.3(Fe_0.7Ti_0.3)_1?x Nb_0.66x O₃ + 1 mol% MnO₂ ceramic with x = 0 exhibits the optimum piezoelectric properties with d ₃₃ = 133 pN C^?1 and k _p = 0.29 and high Curie temperature (T_C = 603^°C).     

Critical Temperature of Smart Meta-superconducting MgB<Subscript>2</Subscript>

Enhancing the critical temperature (T _C ) is important not only to widen the practical applications but also to expand the theories of superconductivity. Inspired by the meta-material structure, we designed a smart meta-superconductor consisting of MgB₂ microparticles and Y₂O₃/Eu³⁺ nanorods. In the local electric field, Y₂O₃/Eu³⁺ nanorods generate an electroluminescence (EL) that can excite MgB₂ particles, thereby improving the T _C by strengthening the electron–phonon interaction. An MgB₂-based superconductor doped with one of four dopants of different EL intensities was prepared by an ex situ process. Results showed that the T _C of MgB₂ doped with 2 wt% Y₂O₃, which is not an EL material, is 33.1 K. However, replacing Y₂O₃ with Y₂O₃/Eu³⁺II, which displays a strong EL intensity, can improve the T _C by 2.8 to 35.9 K, which is even higher than that of pure MgB₂. The significant increment in T _C results from the EL exciting effect. Apart from EL intensity, the micromorphology and degree of dispersion of the dopants also affected the T _C . This smart meta-superconductor provides a new method to increase T _C .     

Heat capacity of the MVO<Subscript>4</Subscript> (M = Al,Ga, In,Tl) orthovanadates

The heat capacity of InVO₄ has been determined by differential scanning calorimetry in the temperature range 339–1089 K. The experimental C_p(T) data have been used to evaluate the thermodynamic functions of indium orthovanadate: enthalpy increment H°(T)–H°(339 K), entropy change S°(T)–S°(339 K), and reduced Gibbs energy Ф°(Т). The specific heats of GaVO₄ and TlVO₄ have been evaluated.     

AC Susceptibility and Superconducting Properties of Graphene Added YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">d</Emphasis></Subscript>

The effect of graphene (G) addition on YBa₂Cu₃O_7?δ(G)_x (x =?0 ? 0.03 wt%) has been studied using the X-ray diffraction method, scanning electron microscopy, electrical resistance versus temperature, transport critical current density J_c, and AC susceptibility measurements. XRD patterns showed single-phase YBa₂Cu₃O_7?δ (YBCO) for all samples. SEM micrographs showed filling of the voids between YBa₂Cu₃O_7?δ grains as graphene was added. The temperature-dependent electrical resistance curves showed metallic normal state behavior and onset transition temperature T_conset between 90 and 92 K for all samples. AC susceptibility measurement showed transition temperature \(T_{\mathrm {c} \chi ^{\prime }}\) between 90 and 93 K. \(T_{\mathrm {c} \chi ^{\prime }}\) was maintained or improved slightly as graphene was added. The x =?0.001 wt% showed the highest J_c, i.e., 2750 A cm^?2 at 77 K and 5570 mA cm^?2 at 30 K which was 13 and 40 times higher than that of the non-added YBCO, respectively. The peak temperature T_p of the imaginary part of the susceptibility χ^″ was around 78–82 K for all samples indicating grain coupling was not weakened as graphene was added.     

Study of the Magnetic Properties of Ni/Ag Superlattice

Thin multilayer films of alternating ultrathin Ni and Ag layers (L(Ni)=11,15,30 Å, bulk and \(L(\mathrm{Ag})=50~{\AA})\) have been prepared by evaporation in ultrahigh vacuum under controlled conditions and have been studied by the magnetic measurements. The critical temperature T _C is studied as a function of the surface exchange interaction (J _S). The dependence of T _C on the thickness L of the film has been investigated. A critical value of the surface exchange interaction in the film, above which the surface magnetism appears, is obtained. The shift of the critical temperature T _C(L) from the bulk value \([\frac{T_{\mathrm{C}}(\infty )}{T_{\mathrm{C}}(L)}-1]\) can be described by a power law L ^?λ , where \(\lambda =\frac{1}{\nu_{\mathrm{b}}}\) is the inverse of the correlation length’s exponent. The effective critical exponent associated with the magnetization M(β) is deduced for different thicknesses of Ni layers, and the thickness L(Ag) was being kept constant at 50 Å.     

Luminescent properties of europium-activated yttrium gadolinium phosphates

Nanocrystalline Y_{1 ? x ? y} Gd _x Eu _y PO₄ phosphors have been prepared via precipitation from aqueous solutions. From their luminescence and excitation spectra, the intensity ratio I ₆₁₅/I ₅₉₄ of the Eu³⁺ luminescence bands corresponding to electric dipole and magnetic dipole transitions has been determined as a function of Gd³⁺ content. The critical concentration and effective energy transfer radius in Y_{1 ? x ? y} Gd _x Eu _y PO₄ have been evaluated. Excitation of Gd³⁺⁸ S _J ?⁶ D _J and ⁸ S _J ?⁶ J _J transitions to Eu³⁺ luminescence excitation levels in Y_{0.99 ? x} Gd _x Eu_0.01PO₄ involves efficient energy transfer. Under 250-nm excitation, the Eu³⁺ luminescence yield in Y_{0.99 ? x} Gd _x Eu_0.01PO₄ is a factor of 2.5–3 higher than that in Y_0.99Eu_0.01PO₄.     

Thermodynamic properties of (TeO<Subscript>2</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>(MoO<Subscript>3</Subscript>)<Subscript>1–<Emphasis Type="Italic">n</Emphasis></Subscript> glasses

The thermal behavior of (TeO₂) _n (MoO₃)_1–n (n = 0.75, 0.85, 0.90) tellurite glasses has been studied by differential scanning calorimetry in the range from T = 300 to T = 850 K and heat capacity has been measured in the temperature range. The thermodynamic characteristics of the devitrification process and glassy state have been determined. The experimental data obtained have been used to evaluate the standard thermodynamic functions of the system in glassy and supercooled liquid states: heat capacity C _p °(T), enthalpy H°(T)–H°(320), entropy S°(T)–S°(320), and Gibbs function G°(T)–G°(320) in the temperature range 320–630 K. The composition dependences of the glass transition temperature and thermodynamic functions for the glasses have been obtained. The thermal and thermodynamic properties of the tellurite glasses have been compared to those of previously studied (TeO₂) _n (WO₃)_1–n and (TeO₂) _n (ZnO)_1–n glasses.     

Synthesis and High-Temperature Heat Capacity of Dy<Subscript>2</Subscript>Ge<Subscript>2</Subscript>O<Subscript>7</Subscript> and Ho<Subscript>2</Subscript>Ge<Subscript>2</Subscript>O<Subscript>7</Subscript>

The Dy₂Ge₂O₇ and Ho₂Ge₂O₇ pyrogermanates have been prepared by solid-state reactions in several sequential firing steps in the temperature range 1237–1473 K using stoichiometric mixtures of Dy₂O₃ (or Ho₂O₃) and GeO₂. The heat capacity of the synthesized germanates has been determined as a function of temperature by differential scanning calorimetry in the range 350–1000 K. The experimentally determined C _p (T) curves of the dysprosium and holmium germanates have no anomalies and are well represented by the Maier–Kelley equation. The experimental C _p (T) data have been used to evaluate the thermodynamic functions of the Dy₂Ge₂O₇ and Ho₂Ge₂O₇ pyrogermanates: enthalpy increment H°(T)–H°(350 K), entropy change S°(T)–S°(350 K), and reduced Gibbs energy Ф°(T).     

Synthesis and High-Temperature Heat Capacity of Neodymium Titanate

Neodymium dititanate, Nd₂Ti2O₇ (monoclinic structure, sp. gr. P2₁), has been prepared by solid-state reaction in air at temperatures from 1673 to 1773 K using the Nd₂O₃ and TiO₂ oxides as starting materials. The high-temperature heat capacity of the resultant polycrystalline Nd₂Ti₂O₇ samples has been determined by differential scanning calorimetry. The experimental C_p(T) data have been used to evaluate the thermodynamic functions of neodymium dititanate (enthalpy increment H°(T)–H°(320 K), entropy change S°(T)–S°(320 K), and reduced Gibbs energy Ф°(T)) in the temperature range 320–1053 K.