晶胞参数的测定.ppt

晶胞参数的测定第一页，共十九页，2022年，8月28日 OutlineExperimental Goal1.Background and Theory2.Example3.第二页，共十九页，2022年，8月28日 Experimental Goal Determine the precise lattice parameters of materials第三页，共十九页，2022年，8月28日 Background and TheoryImportance Useful in determining solid solubility limits of one component in another, coefficients of thermal expansion, and true densities of materials. The magnitudes of changes in the lattice parameters due to a change in solute content or temperature are so small.第四页，共十九页，2022年，8月28日 Background and TheoryA material with a cubic structure第五页，共十九页，2022年，8月28日 Background and TheoryMethodsDebye-Scherrer CamerasDiffractometersMathematizationExtrapolation ＊ Debye-Scherrer Cameras ● Bradley-Jay ● Nelson-Riley ＊ Diffractometers ● ●The least-square method第六页，共十九页，2022年，8月28日 Background and TheoryDebye-Scherrer CamerasSources of error: Film shrinkage Incorrect camera radius Off-centering of specimen Absorption in specimen Divergence of the beam第七页，共十九页，2022年，8月28日 Background and TheoryDiffractometersSources of error: Misalignment of the instrument Use of a flat specimen instead of a specimen curved to conform to the focusing circle Absorption in the specimen Displacement of the specimen from the diffractometer axis Vertical divergence of the incident beam第八页，共十九页，2022年，8月28日 Background and TheoryExtrapolation1. Since varies differently with different errors，a single extrapolation function is not satisfactory in this case．2. It is necessary to have as many reflections as possible in the high-angle region of the diffraction pattern so that you will have many Pointsenabling you to draw the best possible straight line．第九页，共十九页，2022年，8月28日 Background and TheoryThe least-square methodNormal Equations Drift constant第十页，共十九页，2022年，8月28日 ExampleFIG 1．X-ray diffraction pattern of aluminum showing