Thick films of the highT_csuperconducting oxides, LnBa₂Cu₃O₇, Ln = Eu, Y, have been fabricated by screen printing on alumina and SrTiO₃ substrates. Conditions for optimum superconductivity behaviour of the films have been established.T_c^onset varies from 90–94 K for all the films but zero resistance was observed only in a few cases.

The oxygen-deficient phase of the highT_c superconductor, YBa₂Cu₃O₇, was oxygen-enriched using the fluidization technique to give good superconducting properties. The normal method of oxygen treatment at 900°C for 24 h and at 600°C for 24 h has been reduced to just one treatment at 600°C for 12 h by the fluidization technique to achieve almost the same strength of superconducting signal for the YBa₂Cu₃O₇ powder, which establishes the attractiveness of the latter route for the large-scale preparation of superconducting material. The particle sizes were in the range 0–90, 90–180 and 180–420 µm. The fluidized particles were crystalline with orthorhombic distortion.T_c^onset, estimated using the a.c. magnetic susceptibility method, was 91·3 K. The volume fraction of superconducting material in the product was 83·7–85·3%, one of the highest values reported so far for YBa₂Cu₃O₇.

The effect of oxide additives-CuO, SiO₂, Y₂O₃, Bi₂O₃ and ZnO in 1–10 mol% on the sintering and superconducting properties of YBa₂Cu₃O₇ was studied. SEM studies indicated improvement of grain size and interconnectivity due to the additives, the best results being obtained with Bi₂O₃, SiO₂ and Y₂O₃. The superconducting transition temperature is unaffected (92±2 K) even with 10 mol % of the additives. ZnO, however, decreases theT_c as expected.

The layer-type compound, Ca_0·85Sr_0·15CuO₂, which is the prototype of the cuprate family of highT_c oxide superconductors is an electronic insulator, and has a low ordered moment at 300 K indicating that Cu²⁺ ions are highly correlated. Doping with lithium (up tox=0·15) decreases the room temperature resistivity drastically (from 10³ ohm·cm to 0·6 ohm·cm) but metallic behaviour is not induced below 300 K. The magnetic moment on Cu²⁺ remains low but our studies did not show any antiferromagnetic ordering below 300 K in any of the Li-doped phases.

Superconductivity with a maximumT_{c, zero} of 58 K forx > 0·75 has been observed in a nominal starting composition, Th_xTl₂Sr₂Ca₂Cu₃O_y. X-ray data show that the 1212 phase gets stabilized due to part substitution of Th at the Tl-site forx⩾0·25; however,T_c is low forx<0·75.

We have carried out studies on the effect of oxide additives (Ca_0·85Sr_0·15CuO₂, BaBiO₃ and BaPbO₃) on Bi-2212. Compositions up to 6 mole% of all the additives have been prepared and characterized by XRD, resistivity and ac susceptibility techniques. XRD studies indicate that all the materials are single phase. Resistivity and ac susceptibility studies indicate enhanced granular behaviour with the oxide additives. Low temperature (400°) sintering results in degradation of the Bi-2212 phase in the presence of the additives.

The photoelectrochemical behaviour of oxide bronzes of the type A₆Nb₈Ti₂O₃₀ (A = Ba. Sr) has been studied. They show good photoactivity with photopotentials of the order of 700–800 mV. The flat band potential has been estimated to be − 0·9 V vs SCE. The band gap estimated from the spectral response is 3·1 eV.

The structural and magnetic properties of 2 : 17 compounds, their nitrides and carbides and the recent development of the novel 3 : 29 compounds are discussed.

Eu$^{3+}$ photoluminescence (PL) is studied in the tellurooxyphosphate, Ba$_2$TeO(PO$_4$)$_2$, host. A series of phosphor compositions with varying concentrations of Eu$^{3+}$ dopant in Ba$_2$TeO(PO$_4$)$_2$ are synthesized by high temperature solid-state reaction and the PL spectra are recorded. Under 395 nm wavelength excitation, the emission spectrum shows a single peak corresponding to the non-degenerate transition, ${}^5$D$_0$ $\to$ ${}^7$F$_0$ indicating that Eu$^{3+}$ preferentially occupies a singlecrystallographic site. The peak due to the degenerate hypersensitive ${}^5$D$_0$ $\to$ ${}^7$F$_2$ electric dipole transition of Eu$^{3+}$ in theemission spectrum indicates that the site occupied by Eu$^{3+}$ in the tellurooxyphosphate host lattice is non-centrosymmetric. The CIE coordinate values are $x = 0.61$ and $y = 0.34$ and are found to be close to the values of the reference phosphor Y$_2$O$_3$:Eu$^{3+}$.