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We analyse the effect of interplay of the different types of inhomogeneities and the thermal fluctuation of the superconducting order parameter on the excess conductivity in a set of YBa2Cu3O7−y/Ag composite thick films. We show that the mesoscopic inhomogeneities arising due to most of the Ag residing at the grain boundaries strongly influence the tailing and the critical regions below and above the mean field transition temperature, Tc, respectively. A small fraction of Ag diffusing into the grains also produces microscopic inhomogeneities. Though these inhomogeneities are not expected to influence the SCOPF, we found that TLD, corresponding to the transition from the two to three dimensional fluctuation of the order parameter in the mean field region, as well as the inter-planar coupling strength, strongly depend on the Ag content in the composites. The effect of Ag induced inhomogeneities on the temperature window corresponding to different phases in the mean field and the critical regions are depicted in the form of a phase diagram. The large variation of TLD, and near invariance of Tc with Ag content in the films as seen in the phase diagram, are explained by invoking the role of Ag in modifying the overall electronic structure of the grains.

Temperature-dependent electrical resistivity in a set of YBa2Cu3O7/Ag thick films prepared by reaction diffusion technique is analysed to estimate the extent of granularity in them. Percolative nature of charge transfer in the films was examined by studying the excess conductivity in the superconducting order parameter fluctuation (SCOPF) region (T ≥ Tc), the approach to zero-resistance state in the tail region, the current-controlled tailing of the resistivity transition near Tc0(Tc0 < T < Tc0) and the current–voltage characteristics in the paracoherent regime (T < Tc0) with their associated exponents. The percolative current model was thus utilized to quantify granularity in the films of such parameters like the weak link resistivity across grain boundaries, current path lengthening factor arising due to grain misalignment, and due to voids and cracks. Evolution of these parameters with Ag content in the films indicates reduced structural defects (voids and cracks) at higher Ag concentrations. The result points to a mechanism of grain growth in the composites, which accounts for the improved grain growth with narrower grain size distribution in these systems as compared to that in Ag-free YBCO sintered material. These microstructural modifications cause lowering of percolation threshold from the value expected in a granular system where the grain size approaches to one of the system dimensions (the film thickness) making the conduction through grain boundary essentially two-dimensional.

Investigation of defects created in optical grade fused silica due to 200MeV silver ion irradiation is reported. Paramagnetically positively charged oxygen vacancies or neutral dangling Si bonds (E\primecentres), non-bridging oxygen hole centres (NBOHC) and non-paramagnetic defects like B2 bands are observed. The fluence dependent optical and paramagnetic behaviours of these defects are studied using UV–visible absorption spectroscopy, photoluminescence spectroscopy, infrared (IR) absorption and electron paramagnetic resonance. It is observed that generation of E \primecentres, NBOHC and$ B_{2 }$bands gets saturated beyond a fluence of $1 × 10^{12}$ ions $cm^{-2.} $IR spectra showing saturation in transmission at this fluence also support this observation. At this fluence samples get fully covered with latent tracks containing these defects.

In continuation to our earlier studies where we have shown room temperature ferromagnetism observed in TiO2 and Co-doped TiO2 (CTO) thin films independent of their phase (Mohanty et al 2012 J. Phys. D: Appl. Phys. 45 325301), here the modifications in structure and magnetic properties in CTO thin films using 100 MeV Ag7+ ion irradiation are reported. Owing to the important role of defects in tailoring the magnetic properties of the material, we vary the ion fluence from 5 × 1011 to 1 × 1012 ions cm−2 to create post-deposition defects. While the film deposited under 0.1 mTorr oxygen partial pressure retains its crystallinity showing radiation-resistant behaviour even at a fluence of 1 × 1012 ions cm−2, films deposited under 1 to 300 mTorr oxygen partial pressure becomes almost amorphous at the same fluence. Using Poisson's law, the diameter of the amorphized region surrounding the ion path is calculated to be ~4.2 nm from the x-ray diffraction peak intensity ((1 1 0) for rutile phase) as a function of ion fluence. The saturation magnetization (Ms) decreases exponentially similar to the decrease in x-ray peak intensity with fluence, indicating magnetic disordered region surrounding the ion path. The diameter of the magnetic disordered region is found to be ~6.6 nm which is larger than the diameter of the amorphized latent track. Therefore, it is confirmed that swift heavy ion irradiation induces a more significant magnetic disorder than the structural disorder.

TiO2 and Co-doped TiO2 (CTO) thin films deposited at various oxygen partial pressures by pulsed laser deposition exhibit room temperature ferromagnetism (RTFM) independent of their phase. Films deposited at 0.1 mTorr oxygen partial pressure show a complete rutile phase confirmed from glancing angle x-ray diffraction and Raman spectroscopy. At the highest oxygen partial pressure, i.e. 300 mTorr, although the TiO2 film shows a complete anatase phase, a small peak corresponding to the rutile phase along with the anatase phase is identified in the case of CTO film. An increase in O to Ti/(Ti+Co) ratio with increase in oxygen partial pressure is observed from Rutherford backscattering spectroscopy. It is revealed from x-ray photoelectron spectroscopy (XPS) that oxygen vacancies are found to be higher in the CTO film than TiO2, while the valency of cobalt remains in the +2 state. Therefore, the CTO film deposited at 300 mTorr does not show a complete anatase phase unlike the TiO2 film deposited at the same partial pressure. We conclude that RTFM in both films is not due to impurities/contaminants, as confirmed from XPS depth profiling and cross-sectional transmission electron microscopy (TEM), but due to oxygen vacancies. The magnitude of moment, however, depends not only on the phase of TiO2 but also on the crystallinity of the films.

Nanosize TiO2 powders prepared by the sol–gel technique at pH of precipitation 4.5 and 6.5 show the anatase phase after calcining at 500 °C. Anatase to rutile phase transformation (ART), however, occurs at 650 °C in the case of pH 6.5 while 850 °C is found to be the ART temperature for the lower pH sample. pH of precipitation dependent ART temperature has not been reported so far to the best of our knowledge. It is known that the smaller the particle size, the lower the ART temperature, and vice versa. The observation of higher crystallite size and lower ART temperature in the case of the higher pH sample contradicts the reported result. We realized from x-ray photoelectron spectroscopic studies that oxygen vacancy concentration drives the ART temperature to lower values in the higher pH sample compared with the sample synthesized at lower pH; even the particle size is found to be higher in the former one.

Nanocrystalline powders of Zn(1-x)Co(x)O synthesized by the coprecipitation technique show anomalous anisotropic broadening for x>0.05. This peak broadening is shown to be not only due to a reduction in the particle size but also due to a significant strain contribution, as confirmed by Williamson-Hall analysis. The presence of grouped Co(2+) ions, revealing the presence of clusters of high spin Co(2+) with antiferromagnetically coupled spins, as indicated by magnetization studies, seems to be responsible for the strain.

The effect of 200 MeV Ag ion irradiation on the superconducting and normal state properties of the high-Tc superconductor YBa2Cu3O7−y (YBCO) is studied by in situ temperature-dependent resistance measurements. We show that irradiating YBCO thin films (~150 nm) at low temperature result in a softly defected region of about 85 nm radius due to swift heavy ion-induced secondary electrons around the highly amorphized latent tracks of ~5 nm radius. This leads to a decrease of Tc at fluences three orders of magnitude less than the threshold fluence, where overlapping of tracks block the supercurrent path. Due to their low energy (4.1 keV for 200 MeV Ag ions), the secondary electrons can induce point defects by inelastic processes rather than by direct elastic collision.