Papers by Keyword: Lattice Constant

Abstract: A detailed study on the structural and dielectric characterization of the Nd doped SrTiO₃ ceramics at radio frequencies were conducted in this paper. Sr_1-xNd_xTiO₃ (x from 0 to 0.13) ceramics were synthesized using the conventional solid state ceramic route and the phase purity was confirmed through XRD analysis. XRD patterns of the ceramics showed almost similar peaks with no additional phases. A reduction in the lattice parameter can be observed with increase in the Nd content, which can be attributed to the possible lattice shrinkage due to the substitution by a smaller sized ion. The SEM images also showed a reduction in grain size which can be due the fact that Nd doping induces Sr and Ti vacancies in the system which inhibits the grain growth. The dielectric characterization at 1 MHz was done and optimal values of ε_r=5496 and tanδ=0.0925 were observed at x=0.1. Thus the synthesized ceramics can be used for energy storage applications.

Abstract: The spinel ferrite nanoparticles are of great importance to the scientist and technologist. Lithium ferrite is one of the best spinel ferrite used in many technological applications. In the present communication, we report the synthesis of lithium ferrite (Li_0.5Fe_2.5O₄) using sol-gel autocombustion method. Dextrose was used as a chelating agent in the synthesis and the metal nitrates to dextrose ratio was taken as 1:4. The as prepared powder of lithium ferrite was annealed at 550 °C for 4h. A non destructive X-ray diffraction technique was employed to study the phase evolution and crystal structure. The X-ray diffraction pattern was analysed and result suggest that the prepared nanoparticles of lithium ferrite possess single phase cubic structure. No extra peak other than the cubic phase was seen in the XRD pattern. The crystallite size was estimated using Debye Scherrer formula taking into consideration the most intense peak (311) present in the XRD pattern. The full width at half maxima (FWHM) was obtained through (311) plane. The crystallite size was obtained to be 23 nm, indicating the nanocrystalline nature of the prepared samples. The unit cell parameters that is lattice constant obtain from XRD data found to be in good agreement with the reported value. The other structural parameters like hopping length, tetrahedral radius, octahedral radius etc were determined their dependence with lattice constant is discussed in this work.

Abstract: The samples of Eu_2-xCe_xCuO₄ (ECCO) with x = 0.10, 0.13, 0.17 and 0.20 have been synthesized by the solid reaction method without annealing process [1,2]. Each sample is covered by CuO powder to prevent excess oxygen entering the sample during heating process. The purpose of this research is to study the crystal structure and the level of phase purity in ECCO samples in the wide ranges of doping concentration of ECCO. The results of X-ray diffraction (XRD) characterization showed that the main peaks of T' tetragonal structure were observed in all samples. From the XRD analysis, it was found that the level of phase purity of ECCO was 100 % for x = 0.10, 100 % for x = 0.13, 79.5.% for x = 0.17, and 79.1 % for x = 0.20, respectively. For the lattice constant, it is found that both a and c-axis did not change significantly as the concentration increased. These results show that the synthesis method with CuO covering has succeeded in synthesizing materials with high phase purity although the constants do not change significantly when the concentration increased. However, there are some impurity phases found in high concentration of x that is probably due to the existence of excess oxygen, which was not fully absorbed by CuO Covering.

Abstract: Crystal structure and magnetic properties of Heusler-alloy Co₂MnGa were examined systematically using non-stoichiometric compositions of Co and Mn element from the Czochralski as-grown single crystal samples. The crystalline structure of each sample was characterized by means of X-ray powder diffraction technique. Each sample was treated with and without heat treatment at 923 K for 10 hours. The effects of Co and Mn excess were observed in the lattice constants for both treatments. The L2₁-type crystal structure was observed only for the heat-treated samples. The changes in lattice constants are attributed to the substitution of atomic sites. The excess of Co tends to decrease the crystal volume, in opposite to the excess of Mn. In order to investigate the Slater-Pauling rule in the non-stoichiometric samples, the saturation magnetic moments were measured from the field-dependent magnetization measurement for the as-grown samples at 2 K. The deviation from the Slater-Pauling rule was found in the lower concentration of valence electron which associated to the lower total fraction of both Co and Mn. This indicates that the magnetic interactions of these materials cannot only be contributed to the number of valence electron.

Abstract: Crystals of the solid solution Tm(Al_1-xMo_x)B₄ (x = 0.002 - 0.050) were grown from Tm₂O₃, metal Mo and crystalline boron powders as starting materials under an Ar atmosphere at 1773 K for 5 h. Tm(Al_1-xMo_x)B₄ crystals were obtained as a single phase in the case of Al_1-xMo_x flux (x = 0.005 and 0.010). Tm(Al_1-xMo_x)B₄ crystals at a maximum size of about 2.2 mm were obtained in the shape of a flake, and together with needle-like crystals of MoAlB and an unknown phase using Al_0.970Mo_0.030 flux. The lattice constants of Tm(Al_1-xMo_x)B₄ (x = 0.005 - 0.010) crystals were determined to be larger compared to those obtained for TmAlB₄. This is related to the fact that the ionic radius of Mo is larger than the ionic radius of Al. When the Al position in the TmAlB₄ structure was substituted with Mo having a large ionic radius, the hardness hardly changed. In contrast to TmAlB₄, no antiferromagnetic transition could be observed for Tm(Al_0.995Mo_0.005)B₄, indicating that the disorder introduced by Mo-doping disrupted the magnetic transition.

Abstract: Intermetallic compounds are innovative materials and are far superior to conventional metals and alloys. These intermetallic compounds have a great potential in industrial and technological fields because most of the intermetallic compounds are stronger as well asstiffer at elevated temperature and provide far better corrosion resistance than conventional metals and alloys.Over the past few years the scientific interest in the study of these intermetallic compounds emanates greatly because of their high-tech applications. Our motivation of the present studyMgTl mainly consernedon the physical data generation in context with its possible vast applications .We used a theoretical approach within the local density approximation method to study the structural and electronic properties of MgTl by calculating total energy. As far as our calculations are concerned, the band structure shows the overlapping of conduction and valence band thus itis clear that MgTl in its pure form is a good conductor of heat and electricity and falls in the category of metals. We have also calculated lattice parameters, bulkmodules, first order derivative electronic and lattice heat coefficient and Debye temperature.

Abstract: This work extracted the iron-rich phases in aluminium alloy containing the iron of 0.3%, 0.6%, 1%, 0.6%, 2% and 5% respectively, and studied the morphology and the structure of the iron-rich phases by using electrolytic extraction technology. The results showed that the iron-rich phase in aluminium alloy is a large number of alpha - Al₃Fe and a small amount of lambda - Al₁₃Fe₄; the rich iron phases are distributed in aluminum alloy substrate in three-dimensional space, and its metallographic appearances in different sections present sheet, plate and needle-like structure. High resolution electron microscopy shows that lambda - Al₁₃Fe₄ and alpha - Al₃Fe are tetrahedral structure, and when iron content is 0.3% - 1%, the iron-rich phase transition of lambda - Al₁₃Fe₄ to alpha - Al₃Fe is influenced by iron content, and alpha - Al₃Fe lattice constants a and c are bigger than that of standard value under 0.3% iron content, and alpha - Al₃Fe lattice constant a changes little with the increase of iron content, and the lattice constant c becomes larger along with the increase of iron content, and when the iron content is up to 1%, the lattice constant a and c are gradually stabilized; lambda - Al₁₃Fe₄ lattice constant a and c are constant.

Abstract: The electronic structures, densities of states and Fermi surfaces of ErX (X = Cu, Ag and Au) intermetallic compounds are studied using full potential linear augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA) for the exchange-correlation functional. The total energies are computed as a function of volume and fitted to the Birch equation of state. The ground state properties such as equilibrium lattice constants (a₀), bulk modulus (B) and pressure derivative of bulk modulus (B') and density of states at the Fermi level N (E_F) are calculated. The states at the Fermi level (E_F) are dominated by Er ‘d’ states with significant contribution of ‘p’ and ‘d’ states of X. We have also plotted charge density and Fermi surface to study the bonding properties of ErX compounds.

Abstract: We have used full potential linear augmented plane wave method within thegeneralized gradient approximation to investigate the structural, electronic and elastic properties of the AlY. The ground state properties are determined for the AlY. The calculated ground state properties such as lattice constants, bulk modulus and elastic constants agree well with the experimental values. From band structure curves it is found that AlY is metallic in nature. The elastic constants are in good agreement with previous theoretical and experimental results.

Abstract: Using quantum mechanics plane-wave approach based on the density functional theory, the lattice constants of Ni_xAl at different Ni concentrations (x=1, 3) are predicted. Optical properties such as dielectric function, energy loss function and reflectivity are also investigated. Results show that with the increase of Ni constituent, the location of the peak in loss function moves to the lower energy region, but the peak height increases. At 0eV, the reflectivity increases rapidly with the Ni concentration. The reflectivity of NiAl and Ni₃Al are pronounced in the UV region (not in the visible light region). The dielectric properties, namely the real and imaginary parts of the dielectric function, changed significantly with Ni constituent.