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Three fixed-scattering-angle methods for neutron scattering potider measurements using double- and triple-axis crystal spectrometers were tested: (1) the analyzer-scan method (AS), (2) the monochromator-scan method (MS), and (3) the monochromatoranalyzer scan method (MAS). A high-pressure cell, primarily for use in powder diffraction measurements, with scattering angles of 30 , 60 , 90 and 120 and a sample volume of about 0.8 cm was constructed and used in conjunction with the MS and MAS methods. At room temperature, this cell makes it possible to make measurements at pressures up to about 40 kbar and up to about 30 kbar at 300° C. The report includes a description of the diffraction methods and of the high-pressure cell. A few examples of experimental results are also given.

Synchrotron radiation is an excellent tool for studies of structural phase transitions. Among others it enables to follow the transition as a function of the parameter inducing the transition (e.g. pressure, temperature) and time. The latter possibility is due to the short recording times resulting from the high intensity of S.R. For these studies simultaneous recording of the whole diffraction pattern is of great importance. This is achieved either by using a monochromatic beam and a position sensitive detector (PSD) or by using x-ray energy dispersive diffraction (XED). The first method is described only briefly because of its analogy to the conventional method. In the XED method one uses a polychromatic "white" incident beam, a fixed scattering angle and an energy dispersive detector. The main characteristics of the method is the simultaneous recording of the whole diffraction pattern and the fixed scattering angle. The XED method is discussed in some detail. Examples of studies of phase transitions using both methods are briefly described.

X-ray energy dispersive diffraction is used mainly for structural characterization of polycrystalline powders and amorphous materials. One of the important features of it is the fixed scattering angle facilitating in particular studies of materials in special environments (e.g., high pressure, high and low temperature). There are two versions of x-ray energy dispersive diffraction. In one - called XED - an incident "white" beam is used and the spectral distribution of the diffracted photons is analyzed by means of a solid state detector. Its important feature is the simultaneous appearance of all reflections. In the other version - called monochromator scan method (MSM) - the incident beam is monochromatic and its wavelength is changed stepwise by rotating the crystal monochromator. The lecture notes describe both versions and present examples of their applications.