Improved electrical properties of Co-doped 0.92NBT–0.04KBT–0.04BT lead-free ceramics

The (1???2x)NBT–xKBT–xBT ternary piezoelectric system has been extensively studied in recent years. However, its electrical performance is far inferior to lead-based counterparts, and could not meet the requirements for practical applications. In this contribution, the 0.92NBT–0.04KBT–0.04BT (abbreviated as NKBT4) ceramics were prepared by traditional solid-state method. The effects of doped cobalt content on the structure and electrical performance of NKBT4 ceramics were studied systematically. The content of Co₂O₃ affects the average grain size, maximum dielectric constant, piezoelectric properties and the ferroelectric responses of the ceramics. It was found that the introduction of cobalt did not affect the phase structure of the ceramics, but is beneficial for the improvement of the dielectric and piezoelectric properties. When x?=?0.2, the piezoelectric coefficient (d₃₃) is around 130 pC/N, which is greatly improved compared to pure NKBT4 ceramics. Besides, a relatively high dielectric constant (ε_r?=?1150) was obtained at the same composition. This work paves a new way for the further development of high performance lead-free piezoelectric ceramics.     

The thermovoltaic effect in variband solid solution Si<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 1)

The thermovoltaic effect in films of variband solid solution Si_1–x Ge _x (0 ≤ x ≤ 1) has been observed for the first time. The samples comprised n-Si–p-Si_1–x Ge _x (0 ≤ x ≤ 1) heterostructures grown by liquid phase epitaxy. An electromotive force within 0.05–0.3 mV and a current of 0.0025–0.0035 μA appeared on heating samples in a temperature range from 40 to 250°C.     

Effect of mechanical depoling on piezoelectric properties of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–<Emphasis Type="Italic">x</Emphasis>BaTiO<Subscript>3</Subscript> in the morphotropic phase boundary region

The effect of mechanical stress on the direct piezoelectric properties of pre-poled (1 ? x)(Na_0.5Bi_0.5)TiO₃–xBaTiO₃ (NBT–xBT) in the range 4% ≤ x ≤ 13% was studied in situ using a mechanical load frame. Prior to mechanical loading, compositions near the morphotropic phase boundary (MPB, x = 6–7% BT) exhibited enhanced ferroelectric and piezoelectric properties compared to compositions further from the MPB. Specifically, the lowest ferroelectric coercive field and highest piezoelectric coefficient within this composition range occur at x = 7% BT. During mechanical compression, the MPB compositions exhibited the lowest depoling stress. The results demonstrate that, while favorable piezoelectric and ferroelectric properties can be obtained at compositions near the MPB, these compositions are also the most susceptible to the effects of mechanical depoling. Ferroelastic domain wall motion is suggested as the primary factor that may be responsible for these behaviors.     

Critical Behavior of La<Subscript>0.67</Subscript>Ba<Subscript>0.33</Subscript>Mn<Subscript>0.95</Subscript>Fe<Subscript>0.05</Subscript>O<Subscript>3</Subscript> Manganite

The critical behavior of perovskite manganite La_0.67Ba_0.33Mn_0.95Fe_0.05O₃ at the ferromagnetic–paramagnetic has been analyzed. The results show that the sample exhibited the second-order magnetic phase transition. The estimated critical exponents derived from the magnetic data using various such as modified d’Arrott plot Kouvel–Fisher method and critical magnetization M(T _C, H). The critical exponents values for the La_0.67Ba_0.33Mn_0.95Fe_0.05O₃ are close to those expected from the mean field model β = 0.504 ± 0.01 with T _C = 275661 ± 0.447 (from the temperature dependence of the spontaneous magnetization below T _C ), γ = 1.013 ± 0.017 with T _C = 276132 ± 0.452 (from the temperature dependence of the inverse initial susceptibility above T _C ), and δ = 3.0403 ± 0.0003. Moreover, the critical exponents also obey the single scaling equation of M(H, ε) = |ε| ^β f _±(H/|ε| ^β+γ ).     

Effect of Sn Doping on the Crystallization Kinetics of Amorphous TlInS<Subscript>2</Subscript> Films

The crystallization of amorphous Sn-doped TlInS₂ films into three polymorphs has been studied by kinematic electron diffraction. The results demonstrate that the crystallization of 30-nm-thick amorphous films produced by thermal evaporation in high vacuum can be described by the Avrami–Kolmogorov equation: V_τ = V₀[1–exp(–kτ^m)]. Kinematic electron diffraction patterns of the TlIn_1–хSn_xS₂ films have been used to assess the effect of doping with Sn on the growth dimensionality and the activation energy for the crystallization of the amorphous films and the unit-cell parameters of the resultant crystalline materials. Doping extends the temperature range and effective activation energy for the crystallization of the amorphous films.     

Nanomagnetics with lasers

Both liquid and vapour phase pulsed laser deposition (PLD) techniques have been used to synthesize nanophase magnetic alloys of CoPt. While the liquid route results in soft phase (disordered fcc) nanoparticles of CoPt near equiatomic composition dispersed in a surfactant-polymer matrix, the conventional vapour phase PLD allows growth of high coercivity nanoscale structures of CoPt on (001) SrTiO₃. The magnetization, M(T), dynamics of the colloidal particles is examined. Two distinct particle distributions are established from analysis of M(T) data, in conformity with results of electron microscopy. In vapour deposited films at low growth rate (～0.4 Å/s), morphology changes from a self-similar fractal to nanodots as the deposition temperature is raised from 700–800°C. The large lattice mismatch between (001) SrTiO₃ and the ac/bc plane of L1₀ ordered phase imparts tensile strain to the films whose morphological manifestations can be suppressed at high growth rates.     

A new niobate-based CaO–2CuO–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> microwave dielectric ceramic composite for LTCC applications

A novel CaO–2CuO–Nb₂O₅ (CCN) ceramic composite was prepared by the solid-state reaction method in the temperature range of 810–890 °C. Typically, the CCN sintered at 870 °C exhibited the excellent microwave properties of ε _r ?=?15.7, Q?×?f?=?28,700 GHz, τ _f = ? 38.4 ppm/°C. The τ _f of CCN was turned to be near zero by adding TiO₂, while the ε _r increased slightly and the Q?×?f decreased. The 0.91CCN–0.09TiO₂ ceramic sintered at 920 °C showed modified properties of ε _r ?=?16.9, Q?×?f?=?21,500 GHz, τ _f = ? 1.6 ppm/°C, which shows potential in LTCC applications.     

Optical properties of silver containing As–S–Se thin films

The As₃₃S_{67- y} Se _y , where y = 0, 16.75, 33.5, 50.25 and 67, amorphous thin films were prepared by vacuum thermal evaporation technique. Range of the silver content dissoluted in films was x = 0 – 25 at. %. The refractive index increase with increasing silver and selenium content. The difference of the refractive index (Δn) between undoped and silver doped films was ～ 0.4 and between As₃₃S₆₇ and As₃₃Se₆₇ was films ～ 0.42. The values of non-linear refractive index grow with increasing silver and selenium content. The difference of optical bandgap, ΔE _g ^opt , between undoped As₃₃S₆₇ and fully dopped films with Ag and Se was ～ 1 eV.     

Folate-conjugated pH-responsive nanocarrier designed for active tumor targeting and controlled release of doxorubicin

A novel type of amphiphilic pH-responsive folate-poly(ε-caprolactone)-block-poly(2-hydroxyethylmethacrylate)-co-poly(2-(dimethylamino)-ethylmethacrylate) (FA-PCL-b-P(HEMA-co-DMAEMA)) (MFP) block copolymers were designed and synthesized via atom transfer radical polymerization (ATRP) and ring opening polymerization (ROP) techniques. The molecular structures of the copolymers were confirmed with ¹H NMR, FTIR and GPC measurements. The critical micelle concentration (CMC) of MFP in aqueous solution was extremely low (about 6.54 mg/L). The in vitro release behavior of DOX-loaded micelles was significantly accelerated when the pH value of solution decreased from 7.4 to 5.0. In vitro antitumor efficiency was evaluated by incubating DOX-loaded micelles with Hela cells. The results demonstrated that this copolymer possessed excellent biocompatibility, and FA-decorated micelles MFP showed higher cellular uptake than those micelles without the FA moiety, indicating their unique targetability. These folate-conjugated biodegradable micelles are highly promising for targeted cancer chemothe-rapy.     

Effects of Ni co-doping concentrations on dielectric and magnetic properties of (Co,Ni) co-doped SnO<Subscript>2</Subscript> nanoparticles

In this work, the dielectric and magnetic properties of (Co, Ni) co-doped SnO₂ nanoparticles were studied using ac impedance spectroscopy and magnetic properties measurement system or quantum design superconducting quantum interference device. Results showed that dielectric constant (ε _r ), dielectric loss (ε″), and ac electrical conductivity (σ _AC ) are strongly frequency dependent. A decrease in frequency was accompanied with an increase in ε _r and ε″ values, whereas, a decrease in the dielectric constant was observed with the increase of Ni co-doping concentration. It was found that the dielectric constant and dielectric loss values decrease, whilst AC electrical conductivity increases with increase in co-doping concentration. Magnetization measurements revealed that the Ni co-doped SnO₂ samples exhibits room temperature ferromagnetism. The results illustrate that (Co, Ni) co-doped SnO₂ nanoparticles have an excellent dielectric, magnetic properties, and high electrical conductivity than those of co-doped samples reported previously, indicating that these (Co, Ni) co-doped SnO₂ materials can be suitable for the purpose of high frequency device and spintronic applications.     

Effect of Ni<Superscript>2+</Superscript> substitution on crystal structure and microwave dielectric properties for MgZrNb<Subscript>2</Subscript>O<Subscript>8</Subscript> ceramics

Monoclinic structured Mg_1?xNi_xZrNb₂O₈ (0?≤?x?≤?0.12) ceramics were synthesized for the first time through traditional solid-state reaction process and pure phase were obtained in all range. Rietveld refinement was used to analyze the crystal structure. With the increase of Ni²⁺ substitution amount, ε _r decreased, Q?×?f rose first then fell, τ _f shifted for the positive direction. Bond ionicity, lattice energy and bond energy were separately calculated to investigate the correlations with microwave dielectric properties. Typically, ceramics samples with the composition of Mg_0.92Ni_0.08ZrNb₂O₈ sintered at 1280 °C for 4 h exhibited the optimum microwave dielectric properties: ε _r ?=?24.58, Q?×?f?=?74534.1 GHz, τ _f ?=???49.11 ppm/°C, which could be a promising material for application.     

Crystal structure,microstructure and microwave dielectric properties of novel MgAl<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>10</Subscript> ceramic

In the present work, a novel MgAl₂Ti₃O₁₀ ceramic was obtained using a traditional solid-state reaction method. X-ray diffraction and energy dispersive spectrometer showed that the main MgAl₂Ti₃O₁₀ phase was formed after sintered at 1300–1450 °C. With rising the sintering temperature from 1300 to 1450 °C, the bulk density (ρ), relative permittivity (ε _r ) and Q?×?f value firstly increased, reached the maximum values (3.61 g/cm³, 14.9, and 26,450 GHz) and then decreased. The temperature coefficient of resonator frequency (τ _f ) showed a slight change at a negative range of ??94.6 to ??83.7 ppm/°C. When the sintering temperature was 1400 °C, MgAl₂Ti₃O₁₀ ceramics exhibited the best microwave dielectric properties with Q?×?f?=?26,450 GHz, ε _r ?=?14.9 and τ _f ?=???83.7 ppm/°C.     

Growth of epitaxial Cd<Subscript>1–<Emphasis Type="Italic">x</Emphasis> </Subscript>Mn<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>Te films

We have studied the growth and structure of epitaxial films of Cd_1–xMn_x (x = 0.03) diluted magnetic solid solutions grown on mica substrates by molecular beam epitaxy and identified conditions for producing n- and p-type epitaxial films. Using an additional Te vapor source and optimizing the substrate temperature in the growth process, we were able to obtain structurally perfect p-type Cd_1–xMn_xTe (x = 0.03) films with clean, smooth surfaces. The growth plane of the films on the mica substrates is (111) of a face-centered cubic lattice and their unit-cell parameter is а = 6.477 Å.     

A Study on the Wiedemann-Franz Law in a Granular <Emphasis Type="Italic">s</Emphasis>-Wave Superconductor,Given the Tunneling Between the Grains in Cooper Pair Fluctuation Propagator and Impurity Vertex

The present study tries to investigate Wiedemann-Franz law near and far from the critical temperatures, given the tunneling between the grains in Cooper pair fluctuation propagator and impurity vertex. By means of Dyson’s equation, the Cooper pair fluctuation propagator, L(q kΩ _μ ) and the Cooperon (impurity vertex), λ(q, k, ε ₁, ε ₂), are initially calculated in the presence of tunneling between the grains. Then, the three distinct contributions of density of states, Maki-Thompson, and Aslamazov-Larkin, are calculated in the frameworks of the Green’s functions formalism and the Kubo formula technique. The evaluation is conducted under the limited tunneling conductance between the grains. Findings show that although the tunneling is efficient near the critical temperature, it is not effective when it is far from the critical temperature Compared to that in high temperatures, moreover, the deviation from the Wiedemann-Franz law is much more evident in low temperatures.     

Good electrical performances and impedance analysis of (1 − <Emphasis Type="Italic">x</Emphasis>)KNN–<Emphasis Type="Italic">x</Emphasis>BMM lead-free ceramics

(1 ? x)(K_0.5Na_0.5)NbO₃–xBi(Mg_0.75Mo_0.25)O₃ [(1 ? x)KNN–xBMM] (x?=?0.005, 0.01, 0.02) ceramics were prepared via a solid-state reaction method. X-ray diffraction patterns (XRD) and Raman spectrum showed that a solid solution was formed between the BMM and KNN, which improved the electrical properties of KNN. With increasing the BMM content, the grain firstly increased and then decreased. When x?=?0.01, the ceramics exhibited the optimized microstructure, indicating that there exits an optimal doping component. Temperature dependence of relative permittivity also increases firstly and then decreases. The relative permittivity (ε_r) of ~?1418 in stabilization zone, ε_max?~?4861 at the Curie temperature T _C ~ 394 °C, good temperature stability ?ε/ε_123 °C?≤?±?15% from 123 °C to 348 °C, and the dielectric loss tanδ?≤?0.036 from 109 to 348 °C were obtained for 0.99KNN-0.01BMM ceramics. Conductivity behavior of the (1 ? x)KNN–xBMM was investigated as a function of temperature from 420 to 520 °C and frequency from 40 to 106 Hz, showing that the basic mechanisms of conduction and relaxation processes were thermally activated, and oxygen vacancies were the possible ionic charge transport carriers at higher temperatures.     

Measurements of LiNbO<Subscript>3</Subscript> Properties by Multi-parameter Inversion Based on Acoustic Microcopy

This paper expands on a theoretical model between the mechanical and electrical properties with acoustic characteristics to obtain the theoretical dispersion curve for Y-cut LiNbO₃ piezoelectric plate. The experimental dispersion curve of the LiNbO₃ plate is extracted via V(f,z) analysis through defocusing measurements based on an acoustic microscopy and a lens-less line focusing transducer. The objective function of the inversion depends on the experimental dispersion curve. The inversion method adopts a hybrid particle-swarm-based simulated-annealing (PS-B-SA) optimization, which is used for joint inversion of the mechanical and electrical parameters of LiNbO₃. The theoretical dispersion curve will approach the experimental dispersion curve by constantly modifying the mechanical and electrical parameters in the theoretical model: the elastic constants (C₁₁, C₁₂, C₂₂, C₂₃, C₂₅, C₅₅), piezoelectric constants (e₁₁, e₁₂, e₂₆, e₃₃), and dielectric constants (ε₁₁, ε₂₂). The inversed series of constants are those who make the theoretical dispersion curve most fit the experimental ones. The results show that the inversed mechanical and electrical parameters agree well with the reported values, and the stability and accuracy of the inversion is acceptable. This research provides a useful tool to characterize the mechanical and electrical properties of piezoelectric materials simultaneously.     

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.     

Effect of Ba/Y Molar Ratio on Superconducting Properties of BaTiO<Subscript>3</Subscript>-Doped YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript> Films

YBa₂Cu₃ O _7?δ (YBCO) films with BaTiO₃ (BTO) nanostructures were prepared by using the precursor solutions with different cationic molar ratios of Y:Ba:Cu = 1.0:1.6–2.0:3.0 in the TFA-MOD process. These YBCO films were deposited on (00 l)-oriented LaAlO₃ single-crystal substrates using a spin coater. The high superconducting critical current density (J _C) (77 K, self-filed) of more than 10 MA/cm² for the final BTO-doped YBCO film was obtained. Moreover, the effect of different Ba/Y molar ratios in the precursor solution on superconducting properties of BTO-doped YBCO films was investigated. Compared with the BTO-doped YBCO film deposited by using the precursor solutions with Ba/Y molar ratio of 2.0, an enhancement of J _C in a magnetic field for the film from the solution with Ba/Y molar ratio of 1.9 was achieved. For Ba/Y molar ratios of 1.6 and 1.7, a reduction of J _C in a magnetic field occurred. The J _C enhancement may be mainly ascribed to the enhanced flux pinning by the Y₂Cu₂ O ₅ nanostructures with the optimal number dispersing in YBCO matrix.     

The H-T and P-T Phase Diagram of the Superconducting Phase in Pd:Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>

We study the magnetic field vs. temperature (H – T) and pressure vs. temperature (P – T) phase diagrams of the T _c ≈ 5.5 K superconducting phase in Pd _x Bi₂Te₃ (x ≈ 1) using electrical resistivity versus temperature measurements at various applied magnetic fields (H) and magnetic susceptibility versus temperature measurements at various applied magnetic fields (H) and pressure (P). The H – T phase diagram has an initial upward curvature as observed in some unconventional superconductors. The critical field extrapolated to T = 0 K is H _c (0) ≈ 6–10 kOe. The T _c is suppressed approximately linearly with pressure at a rate d T _c /d P ≈ ?0.28 K/GPa.     

Microwave dielectric properties of Sr<Subscript>0.7</Subscript>Ce<Subscript>0.2</Subscript>TiO<Subscript>3</Subscript>–Sr(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> ceramics

xSr_0.7Ce_0.2TiO₃–(1???x)Sr(Mg_1/3Nb_2/3)O₃ ceramics, referred to xSCT–(1???x)SMN, were successfully produced by conventional solid-state sintered technology. The compounds, belonging to perovskites with a secondary phase of CeO₂, can be detected even with x down to 0.1 of SCT composition. The overall trend for grain growth illustrates the increase with increasing SCT doping level. The Raman peak at 825 cm^?1 splits into two peaks and causes red shift phenomenon. XPS spectra indicate that Ti and Nb ions exist respectively in tetravalence and pentavalence, and Ce ions exist in trivalence and tetravalence. Dielectrics constant (ε _r ) of SCT–SMN ceramics gradually increases with increasing theoretical dielectric polarizabilities. A wider width of the 825 cm^?1 for FWHM of A_1g mode Raman peaks suggests to a lower Q?×?f value. The increasing tolerance factor in agreement with temperature coefficient of resonant frequency (τ _f ), denotes that the rise of perovskite symmetry. The 0.1SCT–0.9SMN ceramic sintered at 1450?°C for 4 h illustrates excellent microwave dielectric properties with ε _r ?~?35.4, Q?×?f?~?11282 GHz and τ _f ?~?1.7 ppm/°C. Activation energies of 0.1SCT–0.9SMN ceramic at 100, 300 and 500 V, are ~0.436, 0.427 and 0.331 eV, respectively, indicative of a decreased trend with external electric field.