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We present the results of a detailed theoretical analysis of neutron inelastic scattering measurements of the crystal-field excitations in PrBa 2 Cu 3 O 7 . Using a scaling procedure we estimate the crystal-field parameters for Pr 3+ from those of Ho 3+ determined from neutron spectra of HoBa 2 Cu 3 O 7 . With the scaled parameters as a starting point and guide we refine a model which is able to account for the main features of the crystal-field spectra of PrBa 2 Cu 3 O 7 , including the position of a peak in the neutron spectrum near 280 meV, presented here for the first time, arising from 3 H 4 to 3 H 5 intermultiplet transitions. The analysis leads us to propose the sequence Γ 4 -Γ 2 -Γ 1 for the symmetries of the levels within the crystal-field-split quasi-triplet ground state, and we show that this level scheme is consistent with the observed magnetic anisotropy. We predict the excitation spectrum of Pr 4+ by scaling the Pr 3+ parameters, and use it to estimate an upper limit of 10% for the concentration of stable Pr 4+ ions on the yttrium site. The prevalence of Pr 3+ is consistent with a magnetic interaction, rather than hole-filling, as the major factor responsible for the absence of superconductivity in PrBa 2 Cu 3 O 7 .

The compounds LaBaRCu 3 O 7+ δ (where R = Nd and Pr) have been prepared as single phase materials but their X-ray patterns show an unusual broadening of the higher angle peaks. The resistivity plots of both compounds show a crossover from semiconducting to metallic behaviour as a function of decreasing temperature. Increased duration or temperature of sintering render them completely semiconducting. Electron diffraction analysis of the Nd sample reveals an inherent inhomogeneity with parts of the sample having a superstructure which is probably the result of cation and/or oxygen/vacancy ordering.

We have measured some of the physical properties of the Nd 2−x Sr x NiO 4+y family below room temperature and find a complicated system in which orthorhombic lattice distortion, oxygen stoichiometry, resistivity and magnetic susceptibility change with strontium doping. As the strontium concentration is increased the materials become stoichiometric and tetragonal without reduction and the conductivity of the samples increases although remaining semiconducting. Some compounds demonstrate an unusual low temperature susceptibility which is either temperature independent or falls slightly below ~ 15 K.

We have measured, by means of neutron inelastic scattering, the ground state crystalline electric field excitations in the system Nd2−xSrxNiO4+y for x = 0 and 0.4. The excitations occur at 8.0, 23, 38 and 49 meV in the undoped compound, and at similar energies for the Sr-doped material. A notable feature of the spectra is the large intrinsic width of the peaks, which could be due to disorder or to exchange interactions with the Ni-O planes.

A series of rare earth cuprates crystallising in the 1113 structure similar to CaBaLaCu 3 O 7 were synthesised and characterised. The compounds CaBaRCu 3 O x (R=La, Pr, Nd and Sm) formed in single phase whereas compounds with the other rare earths were not single phase and resulted in the formation of the 123 phase together with other impurity phases. The stability of the 1113 phase was found to be very sensitive to the preparative conditions and the size of the rare earth ion.