High-pressure synthesis of the electron-excess compound CaSi6

The binary phase CaSi₆ is prepared at a pressure of 10(1) GPa and a temperature of 1520(150) K. X-ray single-crystal structure refinements and powder diffraction data of quenched samples reveal that the compound crystallizes in the orthorhombic crystal system (space group Cmcm, a=4.4953(5) Å, b=10.078(1) Å, c=11.469(1) Å). At ambient pressure, exothermic decomposition into CaSi₂ and Si at 737(5) K indicates that the compound is a metastable high-pressure phase. Physical property measurements reveal that the new hexasilicide is diamagnetic and a bad metallic conductor, with resistivity ρ≈900 μΩ cm at 300 K.     

Structural properties of low-temperature grown ZnO thin films determined by X-ray diffraction and X-ray absorption spectroscopy

The epitaxial growth of ZnO thin films on Al₂O₃ (0001) substrates have been achieved at a low-substrate temperature of 150 °C using a dc reactive sputtering technique. The structures and crystallographic orientations of ZnO films varying thicknesses on sapphire (0001) were investigated using X-ray diffraction (XRD). We used angle-dependent X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to examine the variation of local structure. The XRD data showed that the crystallinity of the film is improved as the film thickness increases and the strain is fully released as the film thickness reached about 800 Å. The Zn K-edge XANES spectra of the ZnO films have a strong angle-dependent spectral feature resulting from the preferred c-axis orientation. The wurtzite structure of the ZnO films was explicitly shown by the XRD and EXAFS analysis. The carrier concentration, Hall mobility and resistivity of the 800 Å-thick ZnO film were 1.84 × 10¹⁹ cm^− 3, 24.62 cm²V^− 1s^− 1, and 1.38 × 10^− 2 Ω cm, respectively.     

Al and Ni co-doped ZnO films with room temperature ferromagnetism,low resistivity and high transparence

Zn_0.91Al_0.07Ni_0.02O and Zn_0.90Al_0.05Ni_0.05O films of about 250 nm thick were deposited on glass substrates at 300 K by co-sputtering with ZnO:Al and Ni targets. The films were annealed in vacuum at 673 K for 2 h and then cooled down to room temperature under a magnetic field of 4.8 × 10⁴ A m⁻¹ applied along the film plane. After this process the films showed room temperature ferromagnetism, a resistivity of about 2 × 10⁻³ Ω cm and an average transmittance of 75% in the visible wavelength range. The films have a wurtzite structure with the c-axis orientation in the film growing direction and consist of thin columnar grains perpendicular to the substrate. A temperature dependence of the resistivity from 2 K to 300 K reveals that the carrier transport mechanism is thermally activated band conduction above 150 K and Mott's variable range hopping below 70 K.     

Correlation study between structural, magnetic and transport properties of annealed Co thin films

This paper presents structural, magnetization and transport properties measurements carried out on as-deposited Co (400 Å) thin film as well as samples annealed in the temperature range 100-500 °C in steps of 100 °C for 1 h. The samples used in this work were deposited on float glass substrates using ion beam sputtering technique. The magnetization measurements carried out using MOKE technique, clearly indicates that as-deposited as well as annealed samples up to 500 °C show well saturation magnetization with applied magnetic field. The as-deposited sample shows coercivity value (H_c) of 26 Oe, and it is increased to 94 Oe for 500 °C-annealed sample. A minimum coercivity value of 15 Oe is obtained for 200 °C annealed sample. The XRD measurements of as deposited films show microcrystalline nature of Co film, which becomes crystalline with increase in annealing temperature. The corresponding resistivity measurements show gradual decrease in resistivity. AFM technique was employed to study the surface morphology of as deposited film as well as annealed thin films. Observed magnetization, and resistivity behaviour is mainly attributed to the (i) change in crystal structure (ii) increase in grain size and (iii) stress relaxation due to the annealing treatment.     

Growth and properties of Ca0.28Ba0.72Nb2O6 single crystals

Calcium barium niobate Ca_0.28Ba_0.72Nb₂O₆ (CBN-28) crystals were successfully grown by the Czochralski method. X-ray powder diffraction experiments indicated that CBN single crystals are tetragonal with a = 12.432(±0.002) Å and c = 3.957(±0.001) Å, which have almost the same structure as the Sr_0.50Ba_0.50Nb₂O₆ (SBN-50) crystal. The thermal expansion coefficient perpendicular to Z-direction had been measured to be 1.25 × 10⁻⁵ K⁻¹ between 293.15 and 572.15 K, and along Z-axis was negative between 298.15 and 543.15 K. The specific heat of the crystal had been measured by the differential scanning calorimetric experiments. The transmittance spectra from 200 to 3200 nm were also measured. The measured temperature dependence of dielectric constants showed that the Curie temperature of the CBN-28 crystals is 260 °C, which is about 200 °C higher than that of the (SBN) crystal.     

Bi4LnNb3O15 (Ln = La, Pr, Nd) and Bi4LaTa3O15: New intergrowth Aurivillius related phases

We describe the synthesis and characterization of new intergrowth Aurivillius related phases, Bi₄LnNb₃O₁₅ (Ln = La, Pr, Nd) and Bi₄LaTa₃O₁₅. Both powder X-ray diffraction and electron microscopy investigations show that the compounds adopt orthorhombic structures with the cell parameters a ∼ 5.5 Å, b ∼ 5.5 Å and c ∼ 20.9 Å, suggesting an ordered intergrowth structure that consists of n = 1 [Bi₂NbO₆]⁻ and n = 2 [Bi₂LnNb₂O₉]⁺ Aurivillius fragments which are stacked alternately along the c-axis. The oxides do not show a second harmonic generation (SHG) response toward 1064 nm laser radiation; they do not show a ferroelectric-paraelectric transition either between 30 and 900 °C in dielectric measurements, indicating a centrosymmetric structure. Optical absorption studies show that the intergrowth phases possess considerably smaller band gaps than the parent Nb₂O₅ and Ta₂O₅.     

New ternary intermetallics RE5Ru3Al2 (RE = La, Ce, Pr): Synthesis, crystal structures, magnetic and electric properties

Intermetallics RE₅Ru₃Al₂ (RE = La, Ce, Pr) were prepared by arc melting of the elemental components with subsequent annealing at 820 K. The crystal structures were determined from single-crystal (Ce₅Ru₃Al₂, Pr₅Ru₃Al₂) and powder (La₅Ru₃Al₂) X-ray diffraction at room temperature. The compounds belong to new structural types: space group R3, Z = 6, a = 13.9270(3) Å, c = 8.3260(2) Å for Ce₅Ru₃Al₂ and space group I2₁3, Z = 4, a = 9.95419(6) Å and 9.8084(3) Å for La₅Ru₃Al₂ and Pr₅Ru₃Al₂, respectively. The trigonal structure of Ce₅Ru₃Al₂ is a distorted variant of the cubic La₅Ru₃Al₂ and Pr₅Ru₃Al₂ structures. An interesting feature of the Ce₅Ru₃Al₂ are the short (2.5299(16) Å and 2.5969(15) Å) Ce-Ru distances. Magnetic measurements revealed the Pauli paramagnetic behavior in La₅Ru₃Al₂ and the Curie-Weiss paramagnetism in Pr₅Ru₃Al₂. The latter compound likely exhibits a kind of magnetically ordered state below 24 K. In turn, Ce₅Ru₃Al₂ remains paramagnetic down to 4.2 K and shows signs of mixed valence states of Ce ions. Electrical resistivity measurements indicated simple metallic conductivity in La₅Ru₃Al₂ and Pr₅Ru₃Al₂, and a more complex metallic behavior in Ce₅Ru₃Al₂.     

Elaboration and characterization of Co doped, conductive ZnO thin films deposited by radio-frequency magnetron sputtering at room temperature

Nanocrystalline, highly (at.%) Co doped ZnO powder, obtained by a modified sol-gel method, was used as a target material for the growth of µm thin films by radio frequency magnetron sputtering. The films were deposited at room temperature on quartz substrates. The as-deposited films were polycrystalline but highly textured with the c-axis aligned normal to the substrate plane. They present high optical transmittance in the visible range of approximately 90%, a carrier concentration of about 10²⁰ cm^− 3 and electrical resistivity of 10^− 3 Ω cm at room temperature. The analysis of the Co²⁺ spectrum by electron paramagnetic resonance (EPR) showed the Co to be incorporated substitutionally and the angular variation EPR spectrum demonstrates a monocrystal like texturing of the films with the c-axis normal to the film plane.     

Structural, thermal, magnetic and electrical studies of the iron oxophosphate Rb7Fe7(PO4)8O2·2H2O

A new iron oxophosphate of composition Rb₇Fe₇(PO₄)₈O₂·2H₂O has been synthesized and studied by X-ray diffraction, TG and DTA analysis, magnetic susceptibility, neutron diffraction, Mössbauer spectroscopy and ionic conductivity. This compound crystallizes in the monoclinic system with the P2₁/c space group and the unit cell parameters a = 8.224(8) Å, b = 22.162(6) Å, c = 9.962(6) Å and β = 109.41(8)°. Its structure is built up from Fe₇O₃₂ clusters of edge- and corner-sharing FeO₅ and FeO₆ polyhedra. Neighboring clusters are connected by the phosphate tetrahedra to form a three-dimensional framework. The Rb⁺ cations and the water molecules are occupying intersecting tunnels parallel to a and c. The presence of water molecules was confirmed by TG and DTA analysis. The magnetic susceptibility measurements have shown the existence of antiferromagnetic ordering below 22 K with a weak ferromagnetic component. Additionally, these measurements show evidence for a strong magnetic frustration characterized by |θ/T_N| ≈ 12. Powder neutron diffraction study confirms the presence of a long range antiferromagnetic order coupled to a weak ferromagnetic component along the b-axis. The strongly reduced magnetic moments extracted from the refinement support the existence of a magnetically frustrated ground state. The Mössbauer spectroscopy results confirmed the presence of only Fe³⁺ ions in both five and six coordination. The ionic conductivity measurements led to activation energy of 0.81 eV, a value that agrees with the obtained for other rubidium phosphates.     

Fabrication and dielectric property of ferroelectric PLZT films grown on metal foils

We have grown ferroelectric Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT) films on platinized silicon and LaNiO₃-buffered nickel substrates by chemical solution deposition using a sol-gel process based on acetic acid chemistry. The following measurements were obtained under zero-bias field: relative permittivity of ≈960 and dielectric loss of ≈0.04 on the PLZT film grown on Pt/Si substrates, and relative permittivity of ≈820 and dielectric loss of ≈0.06 on the PLZT film grown on LNO-buffered Ni substrates. In addition, a relative permittivity of 125 and dielectric loss of 0.02 were measured at room temperature under a high bias field of 1 × 10⁶ V/cm on PLZT deposited on LNO-buffered nickel substrate. Furthermore, a steady-state leakage current density of ≈8.1 × 10⁻⁹ A/cm² and mean breakdown field strength of 1.7 × 10⁶ V/cm were measured at room temperature. Finally, remanent polarization (P_r) of ≈2.0 × 10⁻⁵ C/cm², coercive electric field (E_c) of ≈3.4 × 10⁴ V/cm, and energy density of ≈45 J/cm³ were determined from room-temperature hysteresis loop measurements on PLZT/LNO/Ni film-on-foil capacitors with 250-μm-diameter platinum top electrodes.     

Crystal structure of 1,4?-Dimethoxy-4,1′:4′,1″:4″,1?-quaterphenylene

1,4?-Dimethoxy-4,1′:4′,1″:4″,1?-quaterphenylene crystallizes in space group Pbca with a = 7.4989(5) Å, b = 6.1544(3) Å, c = 40.359(2) Å, V = 1862.6(2) ų, and Z = 4. In the crystal structure the molecules are arranged in layers, which are stacked in the direction of the crystallographic c-axis. The torsion between the molecules in a layer amounts to 69.06° resulting in a herringbone structure. The phenyl rings of the molecule are approximately planar with a torsion angle of 4.64° between the outer and the center rings. UV/Vis transmission measurements of the colorless crystal reveal a band gap of ~ 3.2 eV.     

Microstructure and electric properties of (104)/(014)-oriented Bi3.15Nd0.85Ti3O12 films on Pt (111)/Ti/SiO2/Si by sol-gel method

Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT) thin films with predominant (104)/(014) orientation were fabricated directly on (111)Pt/Ti/SiO₂/Si substrates through a sol-gel process. The volume fraction of (104)/(014)-oriented grains in the film was estimated to be about 65% according to X-ray pole figure. The BNdT film is dense and uniform and consists of columnar grains penetrating the whole film thickness. The (104)/(014)-oriented BNdT film capacitors showed excellent ferroelectric properties with 2P_r = 46.4 μC/cm² and E_c ≈ 140 kV/cm. The films also exhibit excellent piezoelectric property, with high piezoelectric coefficient d₃₃ ≈ 17 pm/V.     

Mn-doped ZnO transparent conducting films deposited by DC magnetron sputtering

Mn-doped zinc oxide (ZnO:Mn) thin films with low resistivity and relatively high transparency were firstly prepared on glass substrate by direct current (DC) magnetron sputtering at room temperature. Influence of film thickness on the properties of ZnO:Mn films was investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that all the deposited films are polycrystalline with a hexagonal structure and have a preferred orientation along the c-axis perpendicular to the substrate. As the thickness increases from 144 to 479 nm, the crystallite size increases while the electrical resistivity decreases. However, as the thickness increases from 479 to 783 nm, the crystallite size decreases and the electrical resistivity increases. When film thickness is 479 nm, the deposited films have the lowest resistivity of 2.1 × 10^− 4 Ω cm and a relatively high transmittance of above 84% in the visible range.     

High-rate synthesis of microcrystalline silicon films using high-density SiH4/H2 microwave plasma

A high electron density (> 10¹¹ cm^− 3) and low electron temperature (1-2 eV) plasma is produced by using a microwave plasma source utilizing a spoke antenna, and is applied for the high-rate synthesis of high quality microcrystalline silicon (μc-Si) films. A very fast deposition rate of ∼ 65 Å/s is achieved at a substrate temperature of 150 °C with a high Raman crystallinity and a low defect density of (1-2) × 10¹⁶ cm^− 3. Optical emission spectroscopy measurements reveal that emission intensity of SiH and intensity ratio of H_α/SiH are good monitors for film deposition rate and film crystallinity, respectively. A high flux of film deposition precursor and atomic hydrogen under a moderate substrate temperature condition is effective for the fast deposition of highly crystallized μc-Si films without creating additional defects as well as for the improvement of film homogeneity.     

Effect of doping with Nd ions on the structural and ferroelectric properties of Ca0.28Ba0.72Nb2O6 single crystal

The crystal structure of Ca_0.28Ba_0.72Nb₂O₆ (CBN-28) crystal with Nd-doping has been determined from X-ray single crystal diffraction data, in the tetragonal system with space group P4bm and the following parameters: a = b = 12.458 Å, c = 3.954 Å, V = 613.688 Å³, and Z = 5. X-ray diffraction results on a Nd-doped CBN-28 single crystal also have demonstrated that Nd³⁺ and Ca²⁺ occupy the same site in the crystal structure. Dielectric and ferroelectric measurements have been performed. Transition from ferroelectric to paraelectric at around 223 °C has been observed. The Nd-doped crystal has a lower Curie temperature (T_m) than that of undoped CBN-28 crystal. The spontaneous polarization (P_s) and coercive electric field (E_c) also decrease compared with their values in the undoped CBN-28 crystal.     

New arsenates (V) NaKAl2O[AsO4]2 and Na2KAl3[AsO4]4

The title compounds have been synthesized by a solid state reaction route using a salt flux. Their crystal structures were determined from single crystal X-ray data. NaKAl₂O[AsO₄]₂ crystallizes with the orthorhombic K₂Fe₂O[AsO₄]₂-type, Pnma, a = 8.2368(6) Å, b = 5.5228(3) Å, c = 17.0160(13) Å and Z = 4, whereas Na₂KAl₃[AsO₄]₄ crystallizes with the orthorhombic K₃Fe₃[AsO₄]₄-type, Cmce, a = 10.5049(9), b = 20.482(2), c = 6.3574(6) Å and Z = 4. The NaKAl₂O[AsO₄]₂ structure is built up of [Al₂As₂O₉]²⁻ layers perpendicular to the c-axis which are separated by A⁺ alkali layers. The [Al₂As₂O₉]²⁻ layers consist of ribbons of edge-sharing AlO₆ octahedra, running along the a direction and which are connected through AsO₄ tetrahedra by sharing corners. The Na₂KAl₃[AsO₄]₄ structure contains [Al₃As₄O₁₆]³⁻ layers perpendicular to the b-axis separated by A⁺ alkali layers. The [Al₃As₄O₁₆]³⁻ layer consists of a layer of corner-sharing AlO₆ octahedra which are also connected to the AsO₄ tetrahedra by sharing corners.     

Synthesis and magnetic properties of AgI intercalated Bi-Ca-Co-O misfit-layer cobalt oxide

We report the synthesis and magnetic properties of the AgI-intercalated misfit-layer cobalt oxide Bi_1.8Ca₂Co₂O_z. The AgI-intercalated Bi_1.8Ca₂Co₂O_z was prepared by the guest exchange reaction from the I₂-intercalated one. SEM-EDX analysis exhibited the stoichiometric ratio of Ag/I and the guest concentration as (AgI)Bi_1.8Ca₂Co₂O_z on the basis of Co = 2. After the AgI intercalation, the lattice parameter along the c-axis calculated from X-ray diffraction patterns was 21.68 Å, which was drastically increased not only from the non intercalated host phase (14.68 Å) but also from the I₂-intercalated phase (18.08 Å). After the AgI intercalation, magnetic susceptibility measurements revealed that the antiferromagnetic Weiss temperature and the effective magnetic moment in Co ion simultaneously decreased compared with the non-intercalated host compound.     

Exhibition of structural flexibility of the infinite layer framework of the prototype compound Ca0.85Sr0.15CuO2 prepared under ambient conditions

The infinite layer compound Ca_0.85Sr_0.15CuO₂ has been synthesized by the sol-gel technique using the acetate gel route. The compound is found to be single-phasic as evidenced from the powder X-ray and electron diffraction measurements. EDAX analysis confirms the presence of homogenous stoichiometric phase pertaining to the composition Ca_0.85Sr_0.15CuO₂. High-resolution electron microscopy (HREM) studies reveal interesting defects in the infinite layer frame work of the system. Apart from the usual strain and shear induced defects observed in the lattice, which is common among the perovskite compounds, the main finding is the defect along [0 1 0], occurring due to the intercalation of extra AO layer in the CuO₂ plane. Such a defect is accommodated in the lattice by the increase in the interplanar distance (which is basically the c-axis parameter) from 3.2 to 3.4 Å in the defective layer. This implies the formation of square pyramidal oxygen co-ordination of copper at the defect site.     

Structural investigation by the Rietveld method of sputtered tungsten carbide thin films

Thin films of tungsten carbides deposited by reactive radio-frequency sputtering were investigated by X-ray diffraction using the Rietveld method. Two films were selected for the structural refinement. One was biased, the other unbiased. The unbiased film was found to consist of a cubic phase WC_1 − x (C_0.9) in the space group Fm3m with a lattice parameter of 4.263 (5) Å. A negative substrate bias of − 40 V leads to a multiphasic film: a cubic phase WC_1 − x with a lattice parameter of 4.301 (6) Å and a hexagonal phase W₂C (P-3m1) with lattice parameters of a = b = 2.787 (1) and c = 4.549 (2) Å. The domain size was found to be of ~ 5 nm. The coexistence of nanocrystalline phases WC_1 − x and W₂C is in accordance with the decrease of the carbon content (WC_0.7) in the biased film.     

Study on the doping effect of Li-doped ZnO film

Zinc oxide (ZnO) is an excellent piezoelectric material with simple composition. ZnO film is applied to the piezoelectric devices because it has high resistivity and highly oriented direction at c-axis. Structural and electrical properties in ZnO films are influenced by deposition conditions. Lithium-doped ZnO (LZO) films were deposited by RF magnetron sputtering method using Li-doped ZnO ceramic target with various ratios (0 to 10 wt.% LiCl dopant). LZO films revealed high resistivity of above 10⁷ Ω cm with smooth surface when they were deposited with 4% LiCl-doped ZnO target under room temperature. However, their c-axis orientation was worse than the c-axis orientation of pure ZnO films. We have also studied on structural, optical and electrical properties of the ZnO films by XRD, AFM, SEM, XPS, and 4-point probe analyses. We concluded that LZO films were deposited with 4 wt.% LiCl-doped ZnO target and were apposite for piezoelectrical application.