High purity α-Pu was studied by X-ray diffraction in a diamond anvil cell up to 62 GPa. A structural phase transition occurs around 40 GPa. The high pressure structure was indexed in a hexagonal lattice of space group P63/m, a = 537.77 pm, c = 445.51 pm at 62 GPa, Z = 8. The bulk modulus B0 of α-Pu was determined as 43(2) GPa, with a pressure derivative B0′ = 15(2).

Neptunium monoselenide transforms to a CsCl-type (B2) allotrope at approximately 23 GPa. Its compressibility data are K0 = 60(3) GPa, K0′ = 2.5(5).

Equipment for high pressure experiments at variable temperatures is described. Measurements of U6Fe at ambient temperature up to 50 GPa show no phase transition. The bulk modulus B0=135 GPa and its pressure derivative (B′0=4.4) were obtained for U6Fe. Measurements of Ce were performed both at ambient temperature up to 64 GPa, and at 93 K up to 43 GPa. The tetragonal bc phase of Ce that forms above 26 GPa is unchanged in the extended pressure range, but shows less compressibility at low temperature.

X-ray diffraction analysis was performed on uranium borides under pressure to study their stability vs. compression as well as to obtain their ambient pressure bulk moduli B0. Their crystalline structures remain stable up to 50 GPa and the mean values of B0 and B01 are 225 GPa and 2.6 for UB2, 181 GPa and 4.8 for UB4, 249 GPa and 3.4 for UB12 respectively.

An overview of pressure-induced structural phase transitions and compressibility of actinide compounds will be given. Systematic trends in the nature of the high-pressure phases, the transition pressures, the hysteresis to retransformation on pressure release, and the compressibility are observed in the family of AnX compounds of B1 (NaCl) structure type. The dioxides studied up to now form high-pressure phases of PbCl2 type. UX2 compounds of Fe2As type also tend to have PbCl2 type high-pressure phases. The Th3P4 type compounds studied up to now did not transform up to 50 GPa. The same is true for ThOS and UOSe up to about 45 GPa. Comparison with rare earth compounds will be made where possible.

High-pressure X-ray diffraction studies were performed on ThOS up to 43.3 GPa and on UOSe up to 47.5 GPa, at room temperature, using a diamond anvil cell and synchrotron radiation. The tetragonal structure (P4/nmm) of these compounds was retained over the whole pressure range. The bulk modulus B0 and its pressure derivative B0′ were determined for each compound.

High-pressure X-ray diffraction using synchrotron radiation has been performed on UP1-x -Sx (X=0.1; 0.25; 0.4) up to 53 GPa UP1-x Sx is a solid solution with a B1 (NaCl) structure. For all compositions a second order phase transition is observed around 10 GPa to a distorted B1 structure of rhombohedral symmetry. For UP1-x Sx with x 0.25 a second phase transition is observed, which takes place in the region of 35 GPa This phase transition occurs when the nearest U-U distance reaches the Hill limit of 330–340 pm. The high-pressure phase seems to have orthorhombic or even monoclinic symmetry. It has some similarities to the high pressure phase of UP. UP1-x Sx 4 shows only weak indications for an additional phase at 53 GPa. In conclusion, we observe that the second phase transition and the bulk modulus B, in UP shift to higher pressure, when phosphorus is replaced by sulfur.

Plutonium monoselenide was studied under high pressure up to 47 GPa, at room temperature, using a diamond anvil cell in an energy dispersive X-ray diffraction facility. At ambient pressure, PuSe has the NaC1-type (B1) structure. The compound has been found to undergo a second-order crystallographic phase transition at around 20 GPa. This phase can be described as a distorted B1 structure, with a rhombohedral symmetry. PuSe transforms to a new phase at around 35 GPa, which can be indexed in the cubic CsCl-type (B2). The volume collapse at this phase transition is 11%. When releasing pressure, we observed a strong hysteresis to the inverse transformation down to 5 GPa. From the pressure-volume relationship, the bulk modulus has been determined to B 0 = 98 GPa and its pressure derivative as B 0 = 2.6. These results are compared to those obtained with other actinide monmictides and monochalcogenides.

Thorium and plutonium dioxides were studied under pressure by the energy dispersive X-ray diffraction method. A double conical slit assembly was used to collect simultaneously the diffracted radiation at five and seven degrees. ThO2 undergoes a phase transformation at 40 GPa. The high-pressure phase remains stable up to 55 GPa, the highest pressure reached in the experiment. For PuO2, a structural transformation occurs near 39 GPa. The observed high-pressure phases of ThO2 and PuO2 exhibit similar diffraction spectra. Like for some other fluorite type compounds, the ThO2 and PuO2 high-pressure phase has been indexed in the PbCl2-type structure. The bulk modulus has been calculated as B0= 262 GPa with a pressure derivative of B0' = 6.7 for ThO2 and as B0 = 379 GPa with B0' = 2.4 for PuO2. The volume decrease at the transition is 12% for PuO2 and 8% for ThO2.

The generalised vibrational density of states G( omega ) has been derived from inelastic neutron scattering measurements for the ternary transition metal-metalloid metallic glass Fe40Ni40B20. Two main energy bands are observed centred around 24 and 63 meV and separated by a shallow pseudo-gap near 50 MeV. The former band is mainly due to transition metal-transition metal interaction, the latter is associated to localised optical modes involving transition metal-boron bonds. Rather small differences, if any at all, have been observed for samples prepared by the metal spinning technique at different velocities of the rotating wheel. The neutron weighted G( omega ) have been used to calculate thermodynamic quantities like the temperature dependence of the specific heat and of the Debye temperature.

By means of inelastic neutron scattering the phonon density of states (PDOS) has been measured for 123-O7 and Bi2Sr2CaCu2O8+δ superconductors and different reference compounds. The transition from a superconducting to a semiconducting material is paralleled by characteristic changes in the PDOS. Our results are discussed on the basis of model calculations and it can be shown that high frequency oxygen vibrations in the CuO sublattice are strongly renormalized in the superconducting compounds.

We report about systematic studies on the phonon spectra of 123 superconductors by means of inelastic neutron scattering using polycrystalline samples. We did not observe any unusual dependence on the temperature, in particular no changes were found when passing through the superconducting transition temperature. In contrast, very pronounced changes in the phonon spectra occur when superconductivity is destroyed by the removal of O or a partial replacement of Cu by Zn. Using small single crystals of YBa2Cu3O7−δ we investigated the phonon dispersion curve up to energies ≈40 meV. The results were used to adjust the parameters of a lattice dynamical model.

By means of inelastic neutron scattering the phonon density of states (PDOS) has been measured for compounds Bi2Sr2(Ca1−xYx)Cu2O8+δ for different values ofx. The transition from a superconducting to a semiconducting material is paralleled by characteristic changes in the PDOS as it was observed before for other HTC ceramics. The results are discussed on the basis of a model calculation and it can be shown that high frequency oxygen vibrations in the Cu−O sublattice are stongly renormalized in the superconducting compound.

From inelastic neutron scattering experiments we determined the generalized phonon density-of-states (PDOS) for the high-T c superconductors ME Ba 2 Cu 3 O 7 (ME = Y, Y .5 Pr .5 ,Nd) and the non-superconducting references YBa 2 Cu 3 O 6 and PrBa 2 Cu 3 O 7 . No indications for a pronounced temperature dependence of spectra or correlations between transition temperatures and particular features in the PDOS were found, although, there is this class of material.

Via inelastic neutron scattering experiments the phonon density of states G(ℏω) of the non-superconducting YBa2(Cu.9Zn.1)3O7 has been determined in order to compare it with the high-Tc material YBa2Cu3O7 (the 1-2-3-07 compound). Their vibrational densities of states display pronounced differences especially between 40 and 60 meV where the Zn doped material shows a strong reduction of intensity. In addition we find a high frequency excitation at 84 meV which lies beyond the cut-off frequency of the high-Tc ceramics and which so far no other 1-2-3-07 material has displayed.

By means of inelastic neutron scattering we have studied the phonon densities of states (PDOS) ofY based 123 superconductors with oxygen concentrations varying between O7 and O6. We find drastic changes in the PDOS above 40 meV which develop in a systematic manner if we switch from superconducting to semiconducting samples. Model calculations clearly show that this cannot be explained solely by structural changes but is likely to reflect strong differences in the electron-phonon coupling.