Keller L
CAMET Research, Inc, Goleta, California 93117, USA.
J Biomed Mater Res. 1995 Nov;29(11):1403-13. doi: 10.1002/jbm.820291112.
Least-square refinement of x-ray powder diffraction patterns analyzed by the Rietveld method can yield structural information which had been unattainable or at least elaborate to obtain by conventional pattern analysis. The Rietveld method calculates a powder pattern on the basis of a structural model as well as the characteristics of the instrument used, and minimizes the differences between the intensities observed and the intensities calculated. The method is applied on patterns produced powders or polycrystalline solids on conventional powder diffractometers. For materials containing more than one crystalline phase with known structures such as hydroxyapatite (HA) and whitlockite (beta-TCP), pattern analysis yields phase quantification without internal or external standards. Refinement of the lattice parameters a0 and c0 determines the degree of dehydroxylation in plasma-sprayed HA coatings. The presence of amorphous Ca phosphates in HA coatings is detected by background modeling. The calculation of entire powder patterns allows discrimination of small concentrations of poorly crystallized Ca phosphate phases against the background, and prevents gross aberrations in estimating secondary phases. Even detect structures such as an OH-deficient HA lattice can be detected through slight differences in diffracted intensity by which the pattern calculated deviates from the pattern observed.
通过Rietveld方法分析X射线粉末衍射图谱的最小二乘法精修能够产生结构信息，而这些信息通过传统图谱分析方法是无法获得的，或者至少是难以详尽获取的。Rietveld方法基于结构模型以及所用仪器的特性来计算粉末图谱，并使观测强度与计算强度之间的差异最小化。该方法应用于在传统粉末衍射仪上由粉末或多晶体制成的图谱。对于含有多种已知结构的晶相（如羟基磷灰石（HA）和白磷钙矿（β-TCP））的材料，图谱分析无需内标或外标即可实现相定量。晶格参数a0和c0的精修可确定等离子喷涂HA涂层中的脱羟基程度。通过背景建模可检测HA涂层中无定形磷酸钙的存在。计算整个粉末图谱能够区分小浓度的结晶不良的磷酸钙相和背景，并防止在估计次生相时出现严重偏差。甚至通过计算图谱与观测图谱在衍射强度上的细微差异，诸如OH缺陷型HA晶格这样的结构也能被检测到。
