Papers by Keyword: Structure Refinement

Abstract: The purpose of the work is influence investigation of modifying Nd₅Mo₃O_16+δ oxygen-conducting fluorite-related compound by lead at the crystal structure and conductivity. The substitution of lead for neodymium was studied by XRD (with structure refinement), scanning electron microscopy, FTIR-spectroscopy and conductivity measurements. The compositions Nd_5-xPb_xMo₃O_16+δ (x = 0 – 1.6) were obtained by a solid state reaction from the oxides. It was determined that single-phase solid solution Nd_5-xPb_xMo₃O_16+δ is formed up to x ≈ 0.82. The Rietveld structure refinement shows that lead is statistically located in the Ln1 and Ln2 positions. The introduction of lead does not significantly affect the nature and values of conductivity.

Abstract: Ternary compound Ti₄ZrSi₃ was prepared by arc melting using a non-consumable tungsten electrode under argon atmosphere, then annealed at 1023K for 30 days, the X-ray powder diffraction data of Ti₄ZrSi₃ was collected on a Rigaku SmartLab X-ray powder diffractometer. The powder patterns of the compound were indexed and structure refinement by using Rietveld method indicate that the Ti₄ZrSi₃ compound crystallizes in the hexagonal structure, space group P6/mcm (No.193) with Mn₅Si₃ structure type, a=b=7.5759(3) Ǻ, c=5.2162(2) Ǻ, V=259.28Ǻ³, Z=2, ρ_x=4.779g cm^-3, the Smith–Snyder FOM F₃₀=148.7(0.0064, 46) and the intensity ratio RIR=1.37. The Rietveld refinement results were R_p = 0.0836, R_wp= 0.1092.

Abstract: The paper considers the features of the manifestation of dynamic strain aging (DSA) effect during severe plastic deformation processing via equal-channel angular pressing of low-carbon steel 10 and during the deformation processing via rolling of steel 20Kh. The deformation mechanisms under different regimes of deformation processing are analyzed. The temperature ranges for the manifestation of the DSA effect during the deformation by rolling of steel 20Kh and by equal-channel angular pressing of steel 10 are established. It is demonstrated that the deformation of low-carbon steels in the temperature range of DSA leads to further structure refinement and, as a consequence, to the enhancement in strength properties.

Abstract: Rare earth-transition metal (R-T) intermetallics have been well used because of their excellent properties. The X-ray diffraction patterns of many new phases in the R-T system have not been extensively studied. A new compound AlCrNi₃Pr was prepared by arc melting using non-consumable tungsten electrode under argon atmosphere, and then annealed at 1023K for 30 days. The X-ray powder diffraction data of AlCrNi₃Pr was collected on a Rigaku SmartLab X-ray powder diffractometer. The powder patterns of the compound were indexed, and the structure refinement by using Rietveld method indicated that the AlCrNi₃Pr compound crystallized in the hexagonal structure, space group P6/mmm (No.191) with PrNi₅ structure type, a=b=5.0553(9) Ǻ, c=4.0763(6) Ǻ, V=90.22Ǻ³, Z=1, ρ_x=7.288g cm^-3, the Smith–Snyder FOM F₃₀=279.1(0.0044, 32) and the intensity ratio RIR=1.23.

Abstract: The present work introduces a novel ultrasonic DC casting process which allows producing billets of hypereutectic Al-Si alloys with greatly refined and uniformly distributed particles of primary Si. In the process, ultrasonic vibrations are introduced into an Al-17Si-0.01~0.03P melt in a hot top positioned on the mold by using a high-amplitude ceramic sonotrode. The hot top design and sonotrode arrangement provided a highly effective cavitation treatment of the melt in the hot top and well-controlled flow in the sump. A simplified model is proposed to explain the obtained results.

Abstract: A new method for analysis of powder diffraction intensity data recently developed by the author has been modified to include the effects of possible statistical errors in the goniometer angle 2Θ. The analytical method is based on the maximum-likelihood estimation. Structure parameters refined by the method for fluorapatite Ca₅(PO₄)₃F, anglesite PbSO₄ and barite BaSO4 have become closer to those obtained by single-crystal structure analyses than the results obtained by applications of a conventional Rietveld refinement to the same powder diffraction data, similarly to the previous analyses, where the errors in 2Θ are not included. The statistical errors about 2Θ are estimated at Δ2Θ = 0.0030º, 0.00099º and 0.0036º from the powder diffraction data sets of fluoroapatite, anglesite and barite, respectively.

Abstract: Abstract. The structure and chemical order of a Heusler alloy of non-stoichiometric composition Ni-Mn-Ga were studied using constant-wavelength (1.538 Å) neutron diffraction at 363K and the diffraction pattern was refined using the FullProf software. At this temperature the structure is austenite (cubic) with Fm space group and lattice constant of a = 5.83913(4) [Å]. The chemical order is of critical importance in these alloys, as Mn becomes antiferromagnetic when the atoms are closer than the radius of the 3d shell. In the studied alloy the refinement of the site occupancy showed that the 4b (Ga site) contained as much as 22% Mn; that significantly alters the distances between the Mn atoms in the crystal and, as a result, also the exchange energy between some of the Mn atoms. Based on the refinement, the composition was determined to be Ni1.91Mn1.29Ga0.8

Abstract: A series of Na₅La(WO₄)₄:M³⁺ (M = Eu, Sm, Bi) phosphors have been synthesized successfully by the solid-state reactions. The corresponding crystal structure and lattice parameters were refined by the Rietveld method, and the impact of doped metal ions upon the structure were also studied. The photoluminescent properties were investigated at room temperature. All the samples were observed a strong red emission under 395nm or 465 nm excitation, and the CIE chromaticity coordinates (x = 0.67, y = 0.33) was found to be close to the National Television Standard Committee (NTSC) standard red, implying high color purity. This kind of tungstate phosphor is a promising candidate as the red phosphor for white light-emitting diodes (WLED).

Abstract: The effect of liquid-die-forging pressure on the microstructure and mechanical properties of A390 sloping swash-plate forming was investigated. It was found that the microstructure and comprehensive mechanical properties of the alloy were effectively improved by the liquid-die-forging pressure applied on the A390 aluminum melt. With continuous increasing of the specific pressure, the grain size of primary silicon gradually decreased, the fraction of eutectic silicon obviously decreased, and its morphology was granular mainly. When the applied pressure was 181 MPa, the size of primary silicon was reduced to about 20 μm. When the casting temperature of the alloy was 820 °C, the mould preheating temperature was 240 °C and the forging casting specific pressure reached 181 MPa, the sloping swash plate without macro-defects, and with the internal compact-gain structure and excellent mechanical properties can be obtained.

Abstract: Single crystals of Na0.44MnO2 (=Na4Mn9O18) have been synthesized by a flux method at 1173 K for the first time. The crystal structure of Na0.44MnO2 has been refined by single-crystal X-ray diffraction method. The framework structure consists of double and triple rutile-type chains of edge-sharing MnO6 octahedra and a single chain of edge-sharing MnO5. The Mn-O bond distance and bond valence analyses revealed the manganese valence Mn3+/Mn4+ ordering in the Na0.44MnO2 structure.