Detail Synthesis Route of Free-Standing Antiferromagnetic La2CuO4 Nanoparticles via Sol-gel Method

We report the detailed synthesis route of free-standing antiferromagnetic La2CuO4 nanoparticles by the sol-gel method. The precursors were needed to be dissolved in acid solution and continued with heating treatment to make a gel. Some catalyst was needed to control and stabilized the transformation from the solution to gel. Some heating treatments were also conducted to remove the organic component and for the nucleation process to obtain the single-phase sample. Although the sol-gel method required some additional precursors such as acid and catalyst, it has some advantages. It needed a relatively low sintering temperature and short sintering time compare to those at the solid-state reaction. Interestingly, this method can produce a sample with a good distribution of the particle size.

Incommensurately modulated crystal structure of α′ (O′3)-type sodium cobalt oxide Na x CoO2 (x ∼ 0.78)

A single-phase sample of α′ (O′3)-type layered sodium cobalt oxide Na x CoO2 (x ∼ 0.78) was prepared and its incommensurately modulated crystal structure was analyzed using the (3+1)-dimensional superspace approach to the powder neutron diffraction data. The crystal structure of the cobaltate is accurately described based on the superspace group C2/m(α0γ)00, wherein the positions of Na atoms are most significantly modulated in the monoclinic a direction to form an ordered arrangement. Such a displacive modulation causes a quasi-periodic shift of Na atoms from the centers of the NaO6 polyhedra between undulated CoO2 sheets, changing the form of the NaO6 polyhedron from an octahedral coordination (O) to a trigonal prismatic (P) one, via an intermediate capped trigonal prismatic NaO7 coordination (C). At the positions where the Na atoms are most significantly shifted, the neighboring Na atoms are located at almost touching distances. However, the occupation factor of Na atoms becomes zero at such positions, yielding Na-deficient sites V Na, sandwiched either between C and P, or C and C-type polyhedra.

Synthesis and Structural Study of Ferroelectric Material Lead Titanate (PbTiO3)

Lead Titanate PbTiO3, (PT) is technologically important ferroelectric and piezoelectric ceramics. To make PbTiO3, the oxides PbO and TiO2 are combined in a stoichiometric ratio. Solid-state reaction process was used to synthesize the oxides. The calcination temperature was 8500C. The prepared sample has been characterized by XRD techniques with a scanning rate of 6 degree per minutes. The prepared sample PbTiO3 shows crystalline nature, with Tetragonal symmetry, as observed by X –ray measurements. A scanning electron microscope (SEM) was used to examine the surface morphology and grain size of the obtained samples. Micrographs obtained from SEM analysis revealed a single phase sample of well-defined grains.

Structural, magnetic and high frequency (1–6 GHz) parameters of Sr-substituted BaFe2O4 monoferrites synthesized by sol–gel method

In this work, Sr-substituted samples of single-phase spinel monoferrites with chemical formula [Formula: see text] (x = 0.00, 0.33, 0.67, 1.00) were synthesized using sol–gel auto-combustion method. In order to confirm the single-phase formation of these samples, a sample (x = 0.00) was chosen for heat treatment at different temperatures (100, 300, 400, 600 and [Formula: see text]) for 4 h. The heat treated sample was then investigated by X-ray diffraction (XRD) analysis and results showed that a single-phase sample can be successfully synthesized at a temperature of [Formula: see text], which is much lower than that reported in earlier literature for synthesis of same structured samples. All the synthesized samples were then sintered at [Formula: see text] for 4 h to achieve better crystallinity. From XRD patterns, lattice parameters, cell volume and XRD density as a function of Sr-substitution were calculated. Scanning electron microscopy (SEM) results showed that the grain size increased as the temperature was increased. Fourier transform infrared spectroscopy (FTIR) results confirmed the single-phase spinel monoferrites at [Formula: see text]. From M–H loops (x = 0.0, 0.33, 0.67 and 1.00), different magnetic parameters such as saturation magnetization [Formula: see text], remanance [Formula: see text], coercivity [Formula: see text] and magnetic moment [Formula: see text] were calculated. Magnetocrystalline anisotropy constant and Y–K angles of Sr-doped Ba monoferrites were also calculated. In addition, the variation of different dielectric parameters (real permittivity, imaginary permittivity, real permeability, imaginary permeability, ac conductivity and loss tangent) as a function of frequency (1–6 GHz) has been discussed in this work. The results suggest that the synthesized materials have many advantages over previously reported single-phase spinel monoferrites.

Thermal and Electronic Transport Properties of the Half-Heusler Phase ScNiSb

Thermoelectric properties of the half-Heusler phase ScNiSb (space group F 4 ¯ 3m) were studied on a polycrystalline single-phase sample obtained by arc-melting and spark-plasma-sintering techniques. Measurements of the thermopower, electrical resistivity, and thermal conductivity were performed in the wide temperature range 2–950 K. The material appeared as a p-type conductor, with a fairly large, positive Seebeck coefficient of about 240 μV K−1 near 450 K. Nevertheless, the measured electrical resistivity values were relatively high (83 μΩm at 350 K), resulting in a rather small magnitude of the power factor (less than 1 × 10−3 W m−1 K−2) in the temperature range examined. Furthermore, the thermal conductivity was high, with a local minimum of about 6 W m−1 K−1 occurring near 600 K. As a result, the dimensionless thermoelectric figure of merit showed a maximum of 0.1 at 810 K. This work suggests that ScNiSb could be a promising base compound for obtaining thermoelectric materials for energy conversion at high temperatures.

A practical approach to the direct-derivation method for QPA: use of observed powder patterns of individual components without background subtraction in whole-powder-pattern fitting

The direct-derivation (DD) method for quantitative phase analysis (QPA) can be used to derive weight fractions of individual phases in a mixture from the sums of observed intensities along with the chemical composition data [Toraya (2016). J. Appl. Cryst. 49, 1508–1516]. The whole-powder-pattern fitting (WPPF) technique can be used as one of the tools for deriving the observed intensities of individual phases. In WPPF, the observed powder pattern of a single-phase sample after background (BG) subtraction can be used as the fitting function in combination with the fitting functions widely used in Pawley and Rietveld refinements. The direct fitting of the observed pattern is a very useful technique when the target component is a low-crystallinity or amorphous material [Toraya (2018). J. Appl. Cryst. 51, 446–455]. Technical problems in utilizing the BG-subtracted pattern are the uncertainty associated with the determination of BG height and the parameter interaction between the BG function (BGF) and the BG-subtracted pattern in the least-squares fit. In this study, a practical approach in which single-phase observed patterns are used for the direct fitting without subtracting their BG intensities is proposed. In QPA, the contribution of BG intensities can be neutralized by converting the sum of BG-included intensities into the sum of BG-subtracted intensities by multiplying by a conversion factor. When the magnitudes of the conversion factors are almost identical for all components, they can be canceled out under the normalization condition in deriving weight fractions, and they are not required in QPA. The magnitude of the conversion factor for each component can be determined by one of two experimental techniques: using a single-phase powder of the target component or a mixture containing the target component in a known weight ratio. The theoretical basis of the present procedure is given, and the procedure is experimentally verified. In this procedure, the interaction between the BGF and the BG-included observed pattern is negligibly small. Least-squares fitting with a few adjustable parameters is very fast and stable. Accurate QPA could be conducted, as indicated by the average deviation of 0.05% from weighed values in QPA of α-Al2O3 + γ-Al2O3 mixtures with five different weight ratios and 0.4% in QPA of an α-SiO2 + SiO2 glass mixture

Synthesis and Electrical Characterization of 0.8(K,Na)NbO3-0.2(Ba,Ca)(Zr,Ti)O3 Lead-Free Ceramics

In this research, the physical and electrical properties of 0.8K0.5Na0.5NbO3-0.2Ba0.5Ca0.5Zr0.5Ti0.5O3(0.8KNN-0.2BCZT) were characterized. Lead-free material, 0.8KNN-0.2BCZT with and without alkaline excess was synthesized via solid state reaction method. KNN and BCZT were calcined at 700°C and 1200°C for 2 hours respectively and mixed by planetary milling. The mixed powder was recalcined at 1250°C for an hour then sintered at 1150°C, 1200°C and 1250°C for 2 and 4 hours. XRD analysis of 0.8KNN-0.2BCZT for excessive (8% Na, 2% K) sample sintered at 1150°C for 4 hours has single phase showing ABO3structure (A=K, Na, Ba, Ca and B=Ti, Zr, Nb) and multi phases for the other ones. The microstructure analysis (SEM) showed cubic-like grain shape in which excessive sample possessed greater average grain size than other. Dielectric properties and Curie temperature of single phase sample in this research were higher than those of pure KNN. The conductivity analysis reveals two regimes. The first regime (<300°C) showed no significant role of BCZT in KNN and the second one (>300°C) showed that BCZT increased conductivity of KNN and factor dissipation as well.

Intermediate-valent CeCoAl – a commensurate modulated structure with short Ce–Co distances

CeCoAl was synthesized by melting of the elements in a sealed niobium tube in an induction furnace. Annealing of the sample gave access to a single phase sample. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Above 271 K CeCoAl crystallizes in its own structure type in the space group

Structural position and oxidation state of nickel in SrTiO3

The properties of Ni -doped strontium titanate are studied using X-ray diffraction and XAFS spectroscopy. It is shown that regardless of the preparation conditions, the SrTi 1-x Ni x O 3 solid solution and the NiTiO 3 phase are the most stable phases which can coexist. According to the EXAFS data, in the single-phase sample of SrTi 0.97 Ni 0.03 O 3, the Ni atoms substitute for the Ti ones and are on-center. The distortion of the oxygen octahedra is not observed. The XANES spectra analysis shows that the oxidation state of nickel in NiTiO 3 is 2+, and in the SrTi 1-x Ni x O 3 solid solution it is close to 4+. It is shown that the strongest light absorption in doped samples is associated with the presence of tetravalent nickel in the SrTi 1-x Ni x O 3 solid solution. This doping seems the most promising one for solar energy converters that exploit the bulk photovoltaic effect.

Improved structural model of Pb-doped γ-Bi2O3: (Bi23.68Pb0.32)(Bi1.28Pb0.72)O38.48

A polycrystalline single-phase sample with nominal composition Bi24PbO37 was synthesized from Bi2O3 and PbO by a high-temperature solid state reaction at 690 °C for 1.5 h. The compound adopts Bi12SiO20-type structure [cubic, space group I23 (No. 197); a = 10.24957(3) Å] and was refined to Rp = 7.96%, Rwp = 10.4%, Rexp = 8.43%, RB = 3.06%, and S = 1.23. The distributions of Pb2+ and Bi3+ over cationic sites based on the X-ray powder diffraction data were determined using a combination of the Rietveld refinement and bond valence calculations. The results showed that the asymmetric unit contains two mixed cation sites: the fully occupied 24f site and the partly occupied 8c site, with the unit-cell content (Bi23.68Pb0.32)(Bi1.28Pb0.72)O38.48. The structural constraints favor a preference of Pb2+ ion for the 8c site, i.e. only 1.3% of Bi3+ is substituted by Pb2+ at the 24f site and 36% at the 8c site. At the 24f site, the cations are surrounded by 5 + 2 or in a very small amount by 5 + 1 + 2 oxide ions, forming a base bicapped square pyramid or a bicapped highly deformed octahedron, respectively. At the 8c site, the cations with three oxide ions form a trigonal pyramid with the cations at the apex.