6H hexagonal structure of low loss Ba3MTiWO9 (M = Mg, Zn) dielectrics

The crystal structure of Ba₃MTiWO₉ (M = Mg, Zn) oxides has been found to be 6H hexagonal, space group P6₃/mmc, parameters of unit cell: a = 5.7943(1) Å, c = 14.1642(1) Å and a = 5.7993(1) Å, c = 14.1626(1) Å for M = Mg and Zn, respectively. The tungsten and titanium atoms are randomly distributed in pairs of face-sharing octahedra separated by octahedral layers containing magnesium or zinc. It was revealed that the structures are well ordered which is believed to result in a low dielectric loss at a microwave frequency reported for these materials.     

Propagation of a quasi-shear horizontal acoustic wave in Z-Xlithium niobate plates [and conductivity sensor application]

It is found that an acoustic wave which is nearly polarized in the shear horizontal (SH) direction can propagate along the X axis of a Z-cut lithium niobate plate if the ratio h/λ, where h=plate thickness and λ=acoustic wavelength, is less than about 0.5. Attractive properties of this quasi-SH wave include: (1) phase velocity nearly constant for all values of h/λ; (2) ability to propagate in contact with a liquid medium; and (3) electromechanical coupling coefficient as high as 0.15. These properties make the wave attractive for use in a variety of sensor and signal processing applications. An example of sensor applications is illustrated by using the wave to measure conductivity of liquids (aqueous KCl solution). The frequency of a 12-MHz quasi-SH mode oscillator fabricated on a 0.48 wavelength thick Z-X lithium niobate plate is found to vary by more than 80 kHz for variation in KCI concentration from 0 to 0.15%     

Crystal structure and dynamical properties of a new tellurite: AgTlTeO3

The structure of a newly synthesized AgTlTeO₃ crystalline compound has been solved from single crystal X-ray diffraction data and refined to a final reliability factor R1 = 0.037. It was found having an orthorhombic Iba2 space group symmetry with unit cell parameters a = 14.708(7) Å, b = 10.745(6) Å, c = 5.166(3) Å, Z = 8. Its lattice is divided into separated AgTlTeO₃ sheets parallel to [0 1 0] which are formed by TeO₃ pyramids, TlO₄ disphenoids and AgO₆ octahedra sharing either corners or edges. At the same time, from the crystal chemistry point of view, it can be classified as a typical island-type compound made up from molecular-like [TeO₃]²⁻ ortho-anions weakly connected with Ag⁺ and Tl⁺ cations. The vibrational spectra and their interpretations complemented by the calculated elastic properties confirm this classification. The model-estimated piezoelectric constants allow characterizing AgTlTeO₃ as a strong pyroelectric structure.     

Phase relations and magnetic properties of new phases in theFe-Nd-Al and Fe-Nd-C systems and their influence on magnets

The drastic increase in coercivity observed after adding Al in Fe-Nd-B-based magnet alloys seems to originate partially from the occurrence of new Al-stabilized phases in the grain boundary region and at the surface of the Fe₁₄Nd₂B grains. To describe these phases, they were synthesized and their properties were determined. One of these phases is antiferromagnetic with a high susceptibility of 0.05, while a second one is ferromagnetic with an anisotropy field higher than that of the Fe₁₄Nd₂B (Φ) phase. Magnetization is only half of the Φ phase because of a higher Nd content. The phase relations of these phases in the Fe-Nd-Al system are reported. It is pointed out that it is impossible so far to produce hard magnets from Fe-Nd-C by a sintering process due to phase relations and an inhibition of the formation of Fe₁₄Nd₂ C. The low nucleation and growth rate of Fe₁₄Nd₂ C can be accelerated by the addition of small amounts of a fourth element to the Fe-Nd-C material. The stable phase relations reveal the occurrence of new magnetically hard phases as well as very corrosive phases, which make this part of the system unsuitable for hard magnet production     

Structural and dielectric properties of A(Fe1/2Ta1/2)O3 [A = Ba, Sr, Ca]

The complex perovskite oxide barium iron tantalate (BFT), BaFe_1/2Ta_1/2O₃, strontium iron tantalate (SFT), SrFe_1/2Ta_1/2O₃ and calcium iron tantalate (CFT), CaFe_1/2Ta_1/2O₃ are synthesized by a solid-state reaction technique. Rietveld refinement of the X-ray diffraction data of the samples shows that BFT and SFT crystallize in cubic structure, with lattice parameter a = 4.06 Å for BFT and 3.959 Å for SFT, whereas CFT crystallizes in orthorhombic structure having lattice parameters a = 5.443 Å, b = 5.542 Å and c = 7.757 Å. Fourier transform infrared spectra show two primary phonon modes of the samples at around 450 cm⁻¹ and 620 cm⁻¹. The compounds show significant frequency dispersion in its dielectric properties. The complex impedance plane plots of the samples show that the relaxation (conduction) mechanism in these materials is purely a bulk effect arising from the semiconductive grains. The relaxation mechanism of the samples is modelled by Cole-Cole equation. The frequency dependent conductivity spectra are found to follow the power law.     

Dielectric and impedance properties’ studies of the of lead doped (PbO)-Co2Y type hexaferrite (Ba2Co2Fe12O22 (Co2Y))

In the present work, the preparation of a layered magnetic ceramic oxide Ba₂Co₂Fe₁₂O₂₂ (Co₂Y) is described by the solid state reaction method. X-ray diffraction (XRD) technique was used to study the structural properties. The Rietveld refinement method has confirmed a hexagonal crystal structure with lattice parameters (a = b = 5.8560 ? and c = 43.4977 ?; α = β = 90° and γ = 120°). The dielectric and electrical modulus properties were studied over a range of frequency (1 Hz to 1 MHz) and temperature (313–493 K) using the complex impedance spectroscopy (CIS) technique. The impedance plot showed the first semicircle at high frequency which corresponds to grain effect and the second semicircle at lower frequency which corresponds to grain boundary (conduction phenomenon). A complex modulus spectrum was carried out in order to understand the mechanism of the electrical transport process, which indicates that a non-exponential type of conductivity relaxation is present in this material. The values of the activation energy of the compound (calculated both from dc conductivity and modulus spectrum) are very similar, and hence the relaxation process may be attributed to the same type of charge carriers. The study of the dielectric property, conductivity and loss of ferrite materials, as a function of temperature, is important for microwave absorption applications. The protection of sensitive circuits from the interference of external microwave radiation, is an important technological application of these materials.     

Crystal structure and magnetic properties of double perovskite Mn2FeSbO6

The double perovskite Mn₂FeSbO₆ has been synthesized under pressure 6 GPa and temperature 1000 °C. The crystal structure refinement of Mn₂FeSbO₆ was carried out with the GSAS program suite using X-ray diffraction data. XRD pattern of Mn₂FeSbO₆ was indexed with a monoclinic unit cell (space group P2₁/n) with parameters: a = 5.2431(3) Å, b = 5.3935(3) Å, c = 7.6358(5) Å, β = 89.693(2)°, V = 215.927 Å³, Z = 2. It found that Fe and Sb atoms are completely ordered in 2d and 2c positions of double perovskite structure respectively. According to XPS measurements, manganese in this compound is present as Mn²⁺, whiles the iron - as Fe³⁺. Magnetization measurements revealed the presence about 3 mass% of ferromagnetic impurity in the sample. Dependence of AC susceptibility χ″ from temperature showed that magnetic properties compound are determined probably by transformation in antiferromagnetic state below 19.5 K.     

Study of GeYSi1 − Y:H films deposited by low frequency plasma

In this work, we report a study of the optical properties measured through spectral transmission and spectroscopic ellipsometry in Ge:H and Ge_YSi_1 − Y:H (Y ≈ 0.97) films deposited by low frequency (LF) PE CVD with hydrogen (H) dilution. The dilution was varied in the range of R = 20 to 80. It was observed that H-dilution influences in a different way on the interface and bulk optical properties, which also depend on incorporation of silicon. The films with low band tail characterized by its Urbach energy, E_U, and defect absorption, α_D, have been obtained in Ge:H films for R = 50 with E_U = 0.040 eV and α_D = 2 × 10³ cm^− 1 (hν ≈ 1.04 eV), and in Ge_YSi_1 − Y:H films for R=75 with E_U = 0.030 eV and α_D = 5 × 10² cm^− 1 (hν ≈ 1.04 eV).     

Enhanced ferroelectric properties of Pb(Zr0.80Ti0.20)O3/PbO thin films prepared by radio frequency magnetron sputtering

The Pb(Zr_0.80Ti_0.20)O₃ (PZT) thin films with and without a PbO buffer layer were deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by radio frequency (rf) magnetron sputtering method. The PbO buffer layer improves the microstructure and electrical properties of the PZT thin films. High phase purity and good microstructure of the PZT thin films with a PbO buffer layer were obtained. The effect of the PbO buffer layer on the ferroelectric properties of the PZT thin films was also investigated. The PZT thin films with a PbO buffer layer possess better ferroelectric properties with higher remnant polarization (P_r = 25.6 μC/cm²), and lower coercive field (E_c = 60.5 kV/cm) than that of the films without a PbO buffer layer (P_r = 9.4 μC/cm², E_c = 101.3 kV/cm). Enhanced ferroelectric properties of the PZT thin films with a PbO buffer layer is attributed to high phase purity and good microstructure.     

Co-based superstructured nitride alloy films: characteristics andapplications for high frequency heads

Co-based superstructured films composed of 25-nm-thick non-nitride and nitride layers were prepared by N₂ reactive RF sputtering. The films have high 4πM_s=13 kG, a high permeability μ=3000, and a high thermal stability of the magnetic properties. Magnetic heads composed of laminated superstructured films insulated with SiO₂ films were developed for high-frequency operations. The heads show excellent recording capability for narrow gap recording with metal tapes and high reproduction characteristics at frequencies over 10 MHz. They achieve an increase of more than 4 dB in normalized output when compared with conventional laminated-type amorphous film heads. The superstructured nitride film heads are expected to be used in next-generation VCRs, which operate with higher density recording and wider frequency bands     

Atomic and electronic structure of high-energy grain boundaries in silicon and carbon

We have studied the structure and electronic properties of a few high-energy twist grain boundaries, the (0 0 1) φ=53.1°, or Σ5, and the (0 0 1) φ=43.6°, or Σ29, in the covalently bonded systems Si and C by means of tight-binding molecular dynamics. We describe the parallelization of the code and the main results obtained for the structural and electronic properties of the grain boundaries. The role of structural disorder in silicon is compared to the chemical (bonding) disorder in carbon.     

The effect of Ti4+ ions on some magnetic properties of lithium ferrite

Some magnetic properties of the spinel structure compound, Li_0.5+0.5x Ti _x Fe_2.5-1.5x O₄, wherex=0–0.5, have been studied by different methods. The initial permeability, _i, was measured as a function of temperature at a constant frequency of 10 kHz. A maximum value was observed for each composition indicating the Curie temperature,T _c , which decreases with increasing titanium concentration. The magnetization,M, and theB-H loop were measured atRT in the range of magnetizing field from 0–1200 Am^–1 and at constant fieldH=205 Am^–1, respectively. The relative permeability, _r, depends on the magnetizing field and composition. It was found from theB-H loop that the remanence induction,B _r, and the apparent loss energy,P _s, depend on the composition but the coercive force,H _c, is independent of composition.     

Crystal structure and physicochemical properties of a new organic dihydrogenmonoarsenate

A new organic dihydrogenmonoarsenate (C₃H₉N₂O₂)H₂AsO₄ (abbreviate as ECAs) is prepared by reacting H₃AsO₄ with ethyl carbazate. This compound crystallizes in the monoclinic crystal system, space group P2₁/n. Unit cell parameters are a = 4.8370(2) Å, b = 24.6270(2) Å, c = 7.6311(5) Å, β = 92.948(4)°, with, Z = 4 and ρ_m = 1.800 g cm⁻³. The structure is solved, using the direct methods and refined against F² to a reliability R factor of 0.0475. The compound is characterized by infinite [H₂AsO₄]_nⁿ⁻ ribbons, parallel to the a-direction, connected by organic cations and forming layers localized at y = 0 and 1/2. The cohesion of the framework is ensured by hydrogen bonds N(O)-H?O. The thermal properties of the compounds are investigated as well as the IR properties supported by group theoretical analyses.     

Synthesis and crystal structure of [3,5-(CH3O)2C6H3NH3]4P4O12·4H2O

The chemical preparation and crystal structure are given for a new organic-cation cyclotetraphosphate. This compound is triclinic P-1 with the following unit cell parameters: a=7.857(1) Å, b=8.877(2) Å, c=17.271(3) Å, α=93.94(1)°, β=101.75(2)°, γ=103.72(1)° V=1137.0(4) Å³, Z=1 and ρ_cal=1.467 g cm⁻³. The crystal structure has been determined and refined to R=0.037, using 6291 independent reflections. The atomic arrangement can be described by inorganic layers parallel to the (0 0 1) planes, between which the organic entities are located.     

Influence of liquid refrigerant injection on the performance of an inverter-driven scroll compressor

The operation of a scroll compressor at high compression ratios can cause excessively high discharge temperatures, which can be detrimental to the reliability and efficiency of the compressor. In the present study, the performance of an inverter-driven scroll compressor with liquid refrigerant injection was measured with a variation of compressor frequency, injection pressure, and injection location. The influence of the liquid injection on the performance is presented as a function of operating parameters and injection location by comparing the results with those for the non-injection case. It was found that liquid injection under high frequency was very effective at attaining higher performance and reliability of the compressor, but injection under low frequency showed some disadvantages. For high frequency at a given injection ratio, the injection at α=180°, for an injection angle at an injection port, yielded slightly better performance of the compressor as compared to that at α=90°.     

Fabrication and properties of titanium–hydroxyapatite nanocomposites

Titanium–hydroxyapatite nanocomposites with different HA contents (3, 10, 20 vol%) were produced by the combination of mechanical alloying (MA) and powder metallurgical process. The structure, mechanical and corrosion properties of these materials were investigated. Microhardness test showed that the obtained material exhibits Vickers microhardness as high as 1030 and 1500 HV_0.2, which is more than 4–6 times higher than that of a conventional microcrystalline titanium. Titanium nanocomposite with 10 vol% of HA was more corrosion resistant (i_C = 1.19 × 10⁻⁷ A cm⁻², E_C = −0.41 V vs. SCE) than microcrystalline titanium (i_C = 1.31 × 10⁻⁵ A cm⁻², E_C = −0.36 V vs. SCE). Additionally, the electrochemical treatment in phosphoric acid electrolyte results in porous surface, attractive for tissue fixing and growth. Mechanical alloying and powder metallurgy process for the fabrication of titanium–ceramic nanocomposites with a unique microstructure are developed.     

Crystal structure and characterization of a novel organic crystal: 4-Dimethylaminobenzophenone

Single crystals of a novel organic material, dimethylaminobenzophenone were grown from aqueous solution employing the technique of controlled evaporation. Dimethylaminobenzophenone belongs to the monoclinic system, with a = 12.5755(7) Å, b = 7.9749(4) Å, c = 13.0946(7) Å, α = 90°, β = 111.6380(10)° and γ = 90°. Fourier transform infrared study has been performed to identify the functional groups. The transmittance of dimethylaminobenzophenone has been used to calculate the refractive index n; the extinction coefficient K and both the real ?_r and imaginary ?_i components of the dielectric constant as functions of photon energy. The optical band gap of dimethylaminobenzophenone is 2.9 eV. The structural prefection of the grown crystals has been analyzed by high-resolution X-ray diffraction rocking curve measurements. Thermo gravimetric analysis and differential thermal analysis have also been carried out, and the thermal behavior of dimethylaminobenzophenone crystal has been studied. The dielectric properties and mechanical properties have been investigated.     

IR spectra and dielectric properties of Cu–Ge ferrite

The mixed ferrite Cu_1+xGe_xFe_2−2xO₄; where x = 0.0, 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3; was prepared from high purity oxides using the standard ceramic technique. The IR spectra were recorded on the range from 200 to 1000 cm⁻¹. The two primary bands corresponding to tetrahedral ν_A and octahedral ν_B were observed around 575 cm⁻¹ and 400 cm⁻¹, respectively. It was found the threshold frequency ν_th for the electronic transition increases with increasing the Ge content. The Debye's temperature θ_D was calculated and it was found dependent on the type of charge carriers. AC conductivity σ_ac with dielectric properties (dielectric constant ?′, dielectric loss ?″ and loss tangent tan δ) as a function of frequency (f = 10² → 10⁶ Hz) at room temperature have been measured. The dispersion of the dielectric properties was discussed in the light of Koop's phenomenological theory.     

Sintering, microstructure and microwave dielectric properties of rare earth orthophosphates, RePO4 (Re = La, Ce, Nd, Sm, Tb, Dy, Y, Yb)

Various rare earth orthophosphates, such as monazite and xenotime RePO₄ (Re = La, Ce, Nd, Sm, Tb, Dy, Y, Yb) were prepared by a conventional solid-state reaction method. The crystal structure and microstructure of the sintered ceramics were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The dielectric properties were measured in the microwave region using a network analyzer. It was found that the monazite RePO₄ could be sintered near 1400 °C, although the xenotime RePO₄, which had a smaller Re³⁺ ionic radius, could be sintered above 1600 °C. The permittivity (?_r) of the monazite structures was higher than that of the xenotime structures. This difference was explained by the differences in ionic polarizability and bond strength. Both monazite and xenotime rare earth orthophosphates, however, exhibited a high quality factor (Q × f), where Q = 1/tan δ and f is the measuring frequency, of greater than 60,000 GHz. The temperature coefficient of resonant frequency (τ_f) was a negative value, ranging between −17 and −56 ppm/°C.