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The structural changes in the high temperature superconductors (HTSC) samples of the compounds YBa2Cu3O6·95 and La1·83Sr0·17CuO4 under pressure being unirradiated and irradiated by fast neutrons have been studied by the neutron diffraction method. The different anisotropy of crystal lattice compression was found for these compounds in the initial and irradiated states.

The pressure dependence of the crystal structure of a powder sample of Y2Fe15·3Si1·7 was studied in the pressure range from 0 to 2 GPa, using the D-2 diffractometer with hydrostatic liquid pressure cell at the IVV-2M reactor (Ekaterinburg) and DN-12 time-of-flight diffractometer with a sapphire anvil cell at the IBR-2 pulsed reactor (Dubna). Also the pressure dependence of the Curie temperature Tc (P) of the alloy was studied. The correlation between the decreases of both Tc and Fe-Fe interatomic distances in “dumbbell” site 4f under pressure was obtained.

Pressure-induced structural changes in irradiated YBa2cu3Ox (x=6.95) and uninradiated (x=6.91,6.54,6.39) samples have been measured by neutron powder diffraction in a hydrostatic liquid pressure cell. Tc has been measured for irradiated superconductors under pressure. The value of dTc/dP is found to be high (1.5 =bar). Increase in Tc is associated with charge transfer between the CuO2 planes and CuO chains which is reflected by anisotropy of crystal lattice compression.

The design of a titanium-zirconium clamped cylinder-piston type pressure cell for neutron diffraction investigations under hydrostatic pressure up to 10 kbars without supports is described. It is the first time that Freon-11 has been used as a hydrostatic pressure transmitting medium. The following results carried out at the room temperature are presented: the discovery of the transition from I to 111 phase in a LiKSO4 single crystal and the results of the investigation on the influence of pressure upon the structure of the YBaCuO HTSC obtained by means of the powder diffraction method.