Solid State Phenomena Vol. 163

Abstract: The problem of the crystallite size determination for nanomaterials from X-ray diffraction data obtained in asymmetrical GIXD geometry was analyzed. The studies were performed on nanocrystalline MgO powder prepared by sol-gel synthesis. The nanopowder was preliminary characterized from X-ray diffraction pattern registered in classical Bragg-Brentano geometry and electron microscope observation. The estimated crystallite size, calculated form Williamson-Hall method, equals to 5 nm whereas the lattice distortion is negligible (0.1%). The X-ray diffraction patterns were registered in 30-135º 2θ range using tunnel GIXD technique for the incident α angle: 0.25; 0.5; 1; 2.5 and 5 degrees, respectively. Additional broadening of diffraction lines originated from applied geometry was observed. The calculated crystallite size deviate significantly in comparison to results obtained from classical Bragg-Brentano data. Corrections for additional line broadening were determined, which should be applied for accurate crystallite size calculation in studies of thin nanocrystalline layers using GIXD technique.

Abstract: Results of studies on the modification of Al-7%SiMg alloy with a homogeneous modifier obtained by fast cooling of homogeneous modifiers at V=200 K/s are presented in the paper. Homogeneous modifiers are additions designed for modification of the alloys from which they were obtained at 0, 7, 12 and 20% Si. The components were put into a crucible containing liquid Al-Si alloy and kept there for one minute. The effects of cooling rate and w/w concentration of the modifier in the melt on structure and tensile strength, percentage elongation, Brinell hardness, abrasive wear are illustrated graphically. The analysis of the process of hypo-eutectic Al-Si alloy modification with a homogeneous modifier obtained from treated alloy by fast cooling shows that this modifying addition affected structural,physical and mechanical properties of Al-7%SiMg alloy.

Abstract: The paper presents results of investigations aimed at determining the structure of low-temperature tridymite in refractory silica materials. In the initial phase of works, the literature and Internet databases containing structural data of crystalline compounds were reviewed in search of a model of tridymite structure which best fits the one forming in silica materials. The results of reviewing the models of polymorphous tridymite forms which are available in the world literature have been verified by Rietveld method, using a sample of silica material that contained tridymite without cristobalite and residual quartz. On the basis of analyses it was found that tridymite in refractory silica materials occurs in a form of two low-temperature polymorphous forms C1 and F1, instead of one form – Cc, as it was assumed before. The developed model has been used in a quantitative analysis (Rietvield method) of phase composition of several silica refractories.

Abstract: The structure of the Mo-Re alloys containing 30-85 mass % Mo, obtained from the powders of pure metals by pressure sintering, was investigated. Conditions for the formation of the and  phases, which deteriorate properties of these alloys, have been determined.

Abstract: The intermetallic compounds with a skuttedrudite structure were prepared by powder metallurgy methods including mechanical synthesis and pressure sintering. The obtained powders were subjected to milling so as to obtain powders of a nanocrystalline structure. In this work results of phase analysis carried out at particular stages of powders fabrication are presented and the changes in parameters of their crystalline structure are analysed, including the arrangement of X-type atoms within their crystalline lattice which was studied by the Rietveld method.

Abstract: This work presents the results of investigations using Mössbauer spectroscopy technique and XRD, and their interpretation concerning precipitations and transformation of iron carbides and retained austenite stabilization. It also discusses changes in hardened matrix during tempering in relation to previously conducted dilatometric, microscopic and mechanical examinations. This research was carried out using a new high-carbon alloy 120MnCrMoV8-6-4-2 steel, which was designed in 1998, in Phase Transformations Research Group at the AGH UST. The influence of the tempering time on the mechanical and chemical stability of retained austenite and on the products of its transformation, nucleation and solubility of iron carbides and cementite nucleation and growth, was determined.

Abstract: Single phase materials with general formula CdxMeyCr2Se4 (where Me = Mn, Sn) were obtained using solid state synthesis method. Both compounds are ferromagnets with TC =115K (Sn) and 135K (Mn). The values of Curie-Weiss parameter ΘC-W = 135K (Sn) and 145K (Mn) are higher than respective values of TC indicating a presence of competing antiferromagnetic component. The values of lattice parameters are consistent with Sn and Mn replacing Cd. Slight cadmium deficiency has been also observed.

Abstract: We have observed that doping CuCr2Se4 with tin introduces and then increases the tetrahedral deformation of the spinel structure, which can be connected with the Jahn-Teller (JT) distortion due to Cr2+ ions in antiprismatic environment. The presence of Cr2+ is corroborated by the increase of the saturation magnetization above the 6μB value expected for the 2 Cr3+ ions. In the high limit of the high Sn doping the deformation is decreased, which we attribute to elimination of the JT condition by the increased local distortions. With the tin doping the magnetic structure evolves from the ferromagnet, through spin-glass like to the antiferromagnetic due to increased AF coupling in the system. This is corroborated by the decreasing transition temperature and the Curie-Weiss parameter.

Abstract: The polycrystalline Co0.83Fe1.8Se4 compound was obtained using ceramic method. The chemical composition was verified using energy-dispersive X-ray fluorescence spectrometry (EDXRF) and EDS method. X-ray analysis was used to make phase and structure analysis. The Rietveld method was applied for structure refinement. Co0.83Fe1.8Se4 compound crystallized in monoclinic system, space group C . The magnetic susceptibility and magnetization were measured, they revealed ferrimagnetic properties of a sample.

Abstract: The series of ferrites CuCr2-xFexSe4 (x=0.10.5) were obtained as polycrystalline compounds using conventional ceramics sintering method. The stoichiometric amounts of spectrally pure elements were used for synthesis. The phase and structure determination was done using X-ray analysis. The Rietveld method was applied for structure refinement. It occurred that all samples were multi-phase, the main content crystallized in cubic, normal spinel structure.