For RBa2Cu3Oy(R=Ln and Y), the relationship between superconducting transition temperature Tc, overdoping oxygen content Δy, and R was obtained through studies of oxidation under pressure. Tc of RBa2Cu3Oy remains almost unchanged through various levels of overdoping for small inonic radii of R. As the ionic radius of R increases, Tc decreases with the level of overdoping. The decrease changes systematically from Eu to La; the decrease for La is the steepest. This general view is somewhat modified by the temperature of overdoping. Overdoped oxygen seems to settle down on CuO and/or the Y plane depending also on the treating temperature.
Recent advances in the structural study of liquids under high pressure are reviewed. Using x-rays from synchrotron radiation with high energy and high brightness, x-ray diffraction measurements have been successfully performed for various liquids. Differences in the pressure dependences of the structure are discussed between typical liquid metals, such as alkali metals, and liquids in which atoms are bonded covalently.
Applying pressure to hydrogen bonds significantly alters the bonding nature and induces various kinds of phase transitions. They are order-disorder transition, displacive transition, and bond symmetrization, and have intensively been investigated for ice as a prototype of a hydrogen-bonded system. The phase diagram of dense ice recently established at pressures up to 100 GPa and temperatures down to 0 K have revealed new aspects of physics and chemistry relating to the quantum behavior of protons such as tunneling. The phase relations and their physical implications are reviewed in this article.
Pressure-induced phase transitions are described for the cases of iodine, cesium, and zinc. The relation between the structural change and the change in the electronic structure is discussed in terms of metallization, molecular dissociation, and electronic transitions.
In this article, I briefly reviewed the advancements in high pressure reaerach for solid state physics in the 20th century. I describe how significantly quantum mechanics was combined with high pressure to achieve insight into the various properties of solids at low temperatures on the atomic level and to explore new phenomena which could not be unveiled without the application of high pressure available in low temperature and in high magnetic fields.
By use of synchrotron radiation, the powder x-ray diffraction of LnX (Ln=lanthanide, X=P, As and Sb) with a NaCl-type structure has systematically been studied at high pressures. Pressure-induced phase transitions of LnX were found at room temperature. The transition pressure is highest for LnP and lowest for LnSb. In this report the phase transitions of LnSb at high pressure are mainly described. The high-pressure form of LnSb is classified into three groups. The lighter LnSb (Ln=La, Ce Pr and Nd) have a tetragonal structure (distorted CsCl-type) at high pressures. The structure of the high-pressure phase of the middle LnSb (Ln=Sm, Gd and Tb) is unknown. The heavier LnSb (Ln=Dy, Ho, Er, Tm and Lu) shows the typical NaCl-CsCl transition at high pressures. The high-pressure structural behavior of LnX is discussed.
Various forms for the representation of equations of state for high pressure phases are discussed and it is shown that the special form AP1 related to an interpolation between low and high pressure behaviour appears to be most suitable for the representation of “regular” equations of state.