In-situ X-ray Diffraction Study On High Temperature Structure Of Two Kinds Of Ceramic Materials

X-ray diffraction(XRD),which is widely used in every fields of the basic and applied sciences,is one of the important tools in materials science research.In situ X-ray diffraction,on the other hand,may provide more comprehensive information,and it can reflect the true process more accurately.So in situ X-ray diffraction technique has the extremely widespread application value,in many research fields related to applied materials.In this paper,we studied the high temperature structure evolution on two functional ceramic materials through the In-situ X-ray Diffraction at high temperature.Main of the creative results are follows:1.Correlations of the structural evolution and transport property in manganite Sr7Mn4O15 at high temperature are obtained.Temperature dependence of structural evolution for single phase Sr7Mn4O15 is determined using the in-situ X-ray diffraction with Rietveld refinements in the temperature range of 300-1200 K.It's found that thermal expansion of Sr7Mn4O15 lattice parameters increase linearly with temperature.The structure of face-sharing clusters prefers expansion in the transverse,and corner-sharing clusters prefers the stretch in the longitudinal.The position of Sr ions exists variant temperature modulation,along with the abnormal constriction of coordination shell of Sr(2)and Sr(4).we discussed the high temperature transport properties by means of first-principle calculations and high temperature transport measurement.Resistance decreases sharply with increasing temperature at high temperature,which means that the Sr7Mn4O15 is a well candidate in applications as negative temperature coeffcient thermistor.Based on the fitted atomic parameters given from Rietveld refinements,temperature dependent band gap of Sr7Mn4O15 is estimated with first principle calculation,which exhibits a dramatic reduction from 1.141 eV to 0.349 eV with increasing the temperature.Then internal friction experiment is fully proved Sr7Mn4O15 ceramic material structure is very stability.2.Phases and mechanism of liquid-phase sintering of SiC with Al2O3-Y2O3 additive are derived.The phase transition of SiC-AlhO3-Y2O3 system is in-situ studied using hjgh temperature X-ray diffraction Phase information and mechanism of liquid-phase Sintering of SiC are also discussed.Results shows that Al2O3 doesn't react with Y203 below 1400?.As the heating temperature increasing,Y4Al2O9(YAM)and YAlO3(YAP)phase are formed interactively,which is consistent with the phase of Al2O3-Y2o3 system While Y3A15O15(YAG)phase is not detected at any additive contents,which is inconformity with previous research results.SiO2 crystallizes as a result of SiC recrystallization is detected above 1600? in the specimens with a large number of additives,which is the specific construction form of sintering mechanism.In addition,the experimental results show that the best amount of Al2O3-Y2O3 additives is 10wt%under vacuum sintering estimated by scanning electron microscope(SEM).Our experimental results reveal that the SiC liquid phase sintering consists of the following two stages.In the first stage,phase of the yttrium aluminates form above 1500?.In the second stage,SiO2 crystallizes as a result of SiC recrystallization is detected above 1600?in the specimens with a large number of additives.