Dielectric, ferroelectric and piezoelectric properties of 0-3 barium titanate–Portland cement composites

In this work, barium titanate (BT) and cement composites of 0-3 connectivity were produced with BT concentrations of 30%, 50% and 70% by volume using the mixing and pressing method. The dielectric constant (ε _r ) and the dielectric loss (tan δ) at room temperature and at various frequencies (0.1–20 kHz) of the ferroelectric BT-Portland cement composites with different BT concentrations were investigated. The results show that the dielectric constant of BT-PC composites was found to increase as BT concentration increases, and that the highest value for ε _r —of 436—was obtained for a BT concentration of 70%. In addition, the dielectric loss tangent decreased with increasing BT concentration. Moreover, several mathematical models were used; the experimental values of the dielectric constants are closest to those calculated from the cube model. The 0-3 cement-based piezoelectric composites show typical ferroelectric hysteresis loops at room temperature. The instantaneous remnant polarization (P _ir ), at an applied external electrical field (E ₀) of 20 kV/cm (90 Hz) of 70% barium titanate composite, was found to have a value ≈3.42 μC/cm². Furthermore, the piezoelectric coefficient (d ₃₃) was also found to increase as BT concentration increases, as expected. The highest value for d ₃₃ was 16 pC/N for 70% BT composite.     

Shielding of gamma radiation by hydrated Portland cement–lead pastes

Portland cement mixed with different percentages of granulated lead is studied as shields for gamma radiation. The samples are cured at 100% relative humidity for various time intervals. It is found that cement containing 5% lead has the higher attenuation coefficient value. The results are interpreted by study of the bulk density and the compressive strength of the pastes. The formation of more packed structure of tobermorite by lead addition is studied using the XRD analysis and the SEM micrographs.     

Crystallization kinetics and Avrami index of Sb-doped Se–Te–Sn chalcogenide glasses

Bulk amorphous samples of Sb-substituted Se_78?xTe₂₀Sn₂Sb_x (0 < x < 6) have been prepared using melt quench technique. The structure of Se_78?xTe₂₀Sn₂Sb_x (x = 0, 2, 4, 6) glassy alloys has been investigated using X-ray diffraction technique. Calorimetric studies of the prepared samples have been performed under non-isothermal conditions using differential scanning calorimetry (DSC) and glass transition temperature as well as crystallization temperature has been evaluated using DSC scans. The activation energy of crystallization kinetics (E_c) has been determined using model-free approaches such as Kissinger, Ozawa, Tang and Starink methods. The Avrami index (n) and frequency factor (K_o) have been calculated by Matusita and Augis–Benett method.     

Comparison of Properties of Pt/PZT/Pt and Ru/PZT/Pt Ferroelectric Capacitors

Pb（Zr0.4Ti0.6）O3 film prepared by sol-gel spin coating on a Pt/Ti/SiO2/Si substrate is applied to ferroelectric capacitors with Pt or Ru as the top electrode. For the Pt/PZT/Pt and Ru/PZT/Pt ferroelectric capacitors, although with the same ferroelectric film, different top electrode materials incur different properties of PZT capacitors, such as fatigue, leakage, remanent and saturated polarization, except the similar crystal orientations of the PZT film. After 10^10 switch cycles, the remanent polarizations of the Ru/PZT/Pt and Pt/PZT/Pt capacitors decrease to 70% and 84%, respectively. The leakage current density of the latter increases obviously at positive bias after 108 switch cycles, compared with the former. Different materials for the top electrode bring different conditions at the PZT/top electrode interface. The influence of oxygen-vacancy concentration at the PZT/electrode interface and the influence of oxides of the electrode material at the PZT/electrode interface to charge injection can explain the difference of properties of the PZT capacitors with Pt or Ru as the top electrodes.     

Structural and magneto-transport properties of LCMO–STO composites

A manganite matrix-based composite series, (1 ? x)La_0.67Ca_0.33MnO₃(LCMO) ? (x)SrTiO₃ (STO), has been prepared by the solid state route. Influence of STO phase on structural and magneto-transport properties of LCMO phase has been investigated. By X-ray diffraction, scanning electron microscopy, and Fourier transform of infrared spectroscopy, we find that there is no interdiffusion between the LCMO and STO phases. Measurements of resistivity on these samples reveal that the parent sample shows a distinct metal–insulator (M–I) transition of intrinsic type at a temperature close to the Curie temperature, whereas composite samples show two possible transitions, intrinsic as well as extrinsic. The series exhibits a conduction threshold at x = x _m ～ 20%, up to which extrinsic M–I transition temperature decreases along with an increase in extrinsic magnetoresistance; whereas, above x _m these trends of variation are reversed.     

Magnetic and Resonant Properties of Fe–Bi Films

Physics of the Solid State - Film structures in the Fe–Bi system have been studied experimentally. The magnetic state of the two-layer structures is shown by electron magnetic resonance to be...     

Electrical and optical properties of Sb-doped ZnO thin films synthesized by sol–gel method

Sb-doped ZnO thin films with different values of Sb content （from 0 to 1.1 at.%） are deposited by the sol-gel dip- coating method under different sol concentrations. The effects of Sb-doping content, sol concentration, and annealing ambient on the structural, optical, and electrical properties of ZnO films are investigated. The results of the X-ray diffraction and ultraviolet-visible spectroscopy （UV-VIS） spectrophotometer indicate that each of all the films retains the wurtzite ZnO structure and possesses a preferred orientation along the c axis, with high transmittance （〉 90%） in the visible range. The Hall effect measurements show that the vacuum annealed thin films synthesized in the sol concentration of 0.75 mol/L each have an adjustable n-type electrical conductivity by varying Sb-doping density, and the photoluminescence （PL） spectra revealed that the defect emission （around 450 nm） is predominant. However, the thin films prepared by the sol with a concentration of 0.25 mol/L, despite their poor conductivity, have priority in ultraviolet emission, and the PL peak position shows first a blue-shift and then a red-shift with the increase of the Sb doping content.     

Fabrication and characterization of pure and Sn/Sb-doped ZnO thin films deposited by sol–gel method

Undoped and doped ZnO thin films were prepared by sol–gel method and deposited on tin-doped indium oxides (ITO) substrate using spin coating technique. The effects of Sn and Sb dopants on structural and optical properties were investigated. The starting material was zinc acetate dihydrate, 2-methoxyethanol was used as solvent and monoethanolamine (MEA) as stabilizer. ZnO films were doped with 2% and 7% Sn and Sb concentrations. Optical measurements show an important effect of Sn and Sb dopants on optical band gap.     

Thermal Stability of Structure and Properties of Gradient and Gradient-Layered Coatings of the Ti–Al–Si–Cu–N System

Russian Physics Journal - Using the methods of dark-field electron microscopy analysis, energy-dispersive X-ray microanalysis, hardness measurements and scratch testing, the variations of elemental...     

Preparation and Physical Properties of Carbon Nanotubes–PVA Nanocomposites

Nanocomposite materials were prepared by incorporating multiwall carbon nanotubes (MWNTs), obtained by acetylene catalytic chemical vapor deposition (CCVD) on Co/Fe‐modified MgO, within poly(vinyl alcohol) (PVA). Before incorporation, nanotubes were oxidized to obtain better compatibilization with the polymer. It has been found that the addition of COOH‐functionalized and purified MWNTs improves the mechanical response, increases the glass transition temperature, and delays the thermal oxidation of PVA. Furthermore, the PVA crystallinity seems to be enhanced by the presence of nanotubes.     

Pyroelectric effect in layered magnetoelectric PZT/Ni–Zn ferrite composites

The electric response of layered 2-2 connectivity magnetoelectric composites to the action of a modulated heat flow, which is detected by a dynamic method, is studied. The kinetics of the pyroelectric response of the composite material to a pulsed thermal action is calculated. The experimental results and calculation data suggest that a modulated heat action induces a signal due to both the pyroelectric and piezoelectric effects. The latter effect is caused by the mechanical interaction of the layers of lead zirconate titanate ceramic and nickel–zinc (Ni–Zn) ferrite.     

Electrical and Optical Properties of Polyvinyl Chloride–Polyacetylene Copolymer

Technical Physics - The temperature dependence of the conductivity of heat-treated polyvinyl chloride films containing conjugated double carbon–carbon bonds in the chain of its macromolecules...     

Temperature Properties of Dielectric Permittivity and Optical Properties of a Multilayer Structure of Variozone Barium–Strontium Titanate

Physics of the Solid State - Optical properties and the temperature dependence of the permittivity of a multilayer structure of a variozone ferroelectric barium-strontium titanate deposited on a...     

Fabrication and piezoelectricity of 0–3 cement based composite with nano-PZT powder

Lead zirconate titanate (Pb(Zr_0.52Ti_0.48)O₃) (PZT) nano-powder with a perovskite structure was fabricated using sol–gel process. The average crystallite diameter of the PZT powder is calculated to be 23.6 nm and the average agglomerate size is about 200 nm. The 0–3 cement based nano-PZT composites were obtained by pressing the mixture of white cement and the nano-PZT powders under a high pressure followed by steam curing. The properties of the nano-PZT/cement piezoelectric composites have been measured and compared to the PZT/cement composites incorporated with ground coarse PZT particles. The enhanced piezoelectricity of the nano-PZT/cement composites can be attributed to the good connectivity between the nano-PZT particles among the cement matrix.     

Evaluation of thermomechanical properties of epoxy–basalt fibre composites modified with zeolite and silsesquioxane

The aim of this study was to verify the influence of zeolite and silsesquioxane (POSS) addition on thermo-mechanical properties of basalt fiber reinforced epoxy composites. The dynamic mechanical thermal analysis was conducted with different frequencies at bending mode. The mechanical properties were determined at static tensile test and Charpy impact strength method. The structure of composites was determined by scanning electron microscopy. The thermal stability was characterized by thermogravimetric analyses in inert and oxidizing atmospheres. The impact strength and thermal stability of the composites with zeolite and silseqioxane were higher than the reference sample. Thus, these composites can be used as thermally stable materials with high stiffness.     

Hydrothermal-induced oriented growth of Fe–Co alloy and Sm-substituted magnetite nanowire composites

Fe–Co alloy and Sm³⁺-substituted magnetite nanowire composites (Co_xFe_1−x/Co_yFe_1−ySm_zFe_2−zO₄) have been synthesized via a hydrothermal method without using surfactants or templates. The effects of substitution on structure and morphology were investigated by powder X-ray diffraction, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and transmission electron microscopy (TEM). The TEM image shows that the average diameter of the magnetite nanowires is about 40 nm and the length is several micrometers. The z=0.1 composite shows relatively high saturation magnetization (92.3 emu/g) detected by a vibrating sample magnetometer. The possible growth mechanism of the nanowires is discussed on the basis of the crystal structure of the materials. From the perspective of thermodynamics, we explain the postulated mechanism of the hydrothermal reaction.     

Magnetic losses of the soft magnetic composites consisting of iron and Ni–Zn ferrite

Ferromagnetic powders which are surrounded by an electrically insulating film (soft magnetic composites (SMCs)) exhibit unique magnetic properties, such as relatively low magnetic losses and 3D isotropic magnetic behavior. In some electromagnetic applications, including microwave frequency range applications, it is necessary to increase electrical resistivity without any noticeable reduction in magnetic properties. To achieve this purpose, electrically resistant materials, for example, ferrites with acceptable magnetic properties, are suitable candidates. This paper focuses on the effects of the synthesized Ni–Zn ferrite addition on the magnetic properties of the SMCs containing Ni–Zn ferrite within iron particles. The structure was studied by means of X-ray diffraction (XRD). The microstructure and the powder morphology were examined by the use of scanning electron microscopy (SEM). The magnetic measurements on powders and samples were carried out using a vibrating sample magnetometer (VSM) and an LCR meter, respectively. The results indicate that the lowest magnetic loss and the highest magnetic permeability are related to the composites with 20 wt% ferrite and 2 wt% ferrite, respectively. Also, the composites with 10 wt% ferrite show a good combination of magnetic loss and magnetic permeability in the range 0–500 kHz.     

Laser initiation of PETN–iron nanoparticle composites

The dependences of the probability of explosion initiation in pentaerythritol tetranitrate samples with different contents of iron nanoparticles on the fluence of the first- (λ = 1064 nm) and second-harmonic (λ = 532 nm) pulses of a neodymium laser are measured. The laser initiation threshold for PETN–iron nanoparticle composites nonmonotonically depends on the mass fraction of nanoparticles. The optimal values of the mass fraction of iron nanoparticles at which the sensitivity to laser irradiation is maximal (0.4 wt % for the first harmonic and 0.15 wt % for the second) are determined. It is demonstrated that the amplitude of the optoacoustic signal under non-explosion conditions reaches its maximum for composites with the optimal values of the mass fraction of nanoparticles.     

Properties of superconductor–Luttinger-liquid hybrid systems

In this paper, we review some recent results concerning the physics of superconductor–Luttinger-liquid proximity systems. We discuss both equilibrium (the pair amplitude, Josephson current, and the local density of states) and nonequilibrium (the subgap current) properties.