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In this paper we report influence of titanium substitution on the structural properties and d.c. conduction behavior of Li-Zn ferrites. The samples having the compositional formula Li_0.45+0.5tZn_0.1Ti_tFe_2.45-1.5tO₄ with t varying from 0 to 1.2 in steps of 0.2 were prepared by the conventional dry ceramic method. XRD analysis showed all the samples to be single phase spinel and the lattice parameter was found to increase with increasing t. D.C. resistivity increases with Ti concentration. The possible mechanisms involved are discussed.

The influence of partial substitution of Nd by Gd and Ce on the Nd₂CuO₄n-type superconductor was studied by using X-ray diffraction measurements. For x = 0.15 Ce the maximum value of critical transition temperature T_c was obtained. The influence of Gd concentration on the lattice parameters and unit-cell volume was studied in the optimal doped sample (x = 0.15 Ce) and in the samples with 0≤x≤0.2 Ce.

The relation between structural parameters and critical transition temperature was evidenced. The transition from the structural normal phase to the distortion phase was evidenced above y = 0.75 Gd in the optimal Ce-doped sample.

Samples of series Bi_1.6Pb_0.4Sr₂Ca₂Cu_3-xZn_xO_10-δ with x = 0.0, 0.015, 0.03, 0.06, 0.09 and 0.12 are synthesized by solid-state reaction route. All the samples crystallize in tetragonal structure with majority (> 90%) of Bi-2223(Bi₂Sr₂Ca₂Cu₃O₁₀) phase (c-lattice parameter ~ 36 Å). The proportion of Bi-2223 phase decreases slightly with an increase in x. The lattice parameters a and c of main phase (Bi-2223) do not change significantly with increasing x. Superconducting critical transition temperature (T_c) decreases with x as evidenced by both resistivity [ρ(T)] and ac magnetic susceptibility [χ(T)] measurements. Interestingly the decrement of T_c is not monotonic and the same saturates at around 96 K for x > 0.06. In fact T_c decreases fast (~ 10 K/at%) for x = 0.015 and 0.03 samples and later nearly saturates for higher x values. Present results of Zn doping in Bi-2223 system are compared with other Zn-doped HTSC (high temperature superconducting) systems, namely the RE-123 (REBa₂Cu₃O₇) and La-214 ((La, Sr)₂CuO₄).

Samples with representative formula Li_0.45Ni_0.1Mn_0.1Fe_2.35O₄ have been sintered by conventional sintering technique and microwave sintering technique. Both the samples showed single-phase with spinel structure. The lattice constant for the microwave sintered (MS) sample showed a lower value than the conventionally sintered (CS) sample. The density of the MS sample has been found to be higher than the CS sample. And MS sample showed a higher value of resistivity and activation energy compared to the CS sample. The possible mechanisms are discussed.

We investigate the resistivity in high transition temperature superconductors. It was shown that phonon-enhanced spin fluctuations drive this superconductivity once more, as was suggested by us [Phys. Rev. B61, 4289]. The resistivity in the presence of phonon-enhanced spin-flippings, different from pure Kondo ones, was calculated. We compared the resistivity from pure Kondo spins and that from phonon-enhanced spins, which are in good fit with the experimental data of Y-Ba-Cu-O. Using a basic method, different from conventional ones, we also calculated resistivities in other non-superconducting materials.

Electron-doped Sr_1-xLa_xMnO₃(0≤x≤0.50) and hole-doped (x=0.70 and 0.82) samples have been prepared by solid state route. X-ray diffraction patterns could be refined using P6₃ space group for x≤0.30 and space group for x≥0.40. Temperature variation of AC susceptibility measurements show that all the electron-doped materials exhibit paramagnetic to ferromagnetic transitions with the transition temperatures ranging from 375 to 393 K, followed by low temperature antiferromagnetic transitions. The ferromagnetic maximum susceptibility is found to increase systematically with La doping, i.e. with increase in Mn³⁺ ions. The high temperature resistivity data could be analyzed using the Mott-variable range hopping model. The hole-doped materials exhibit ferromagnetic to paramagnetic transition.

Processing of ferrites has gained tremendous importance in recent times in order to meet high performance demands on ferrites in keeping with the fast emerging technologies. The main focus of research in the 21st century is towards the formation of smaller magnetic particles. In normal ceramic methods we cannot control particle size and porosity, whereas in precursor methods we can control both. In the present study we have synthesized Mg_0.9Mn_0.1Fe₂O₄ ferrites by the normal ceramic method and the citrate precursor method. By the citrate method we have simultaneously reduced the particle size and sintering temperature as compared to the normal ceramic method. By the citrate method, direct current (DC) resistivity is increased by two orders of magnitude, and electrical as well as magnetic losses are reduced as compared to the normal ceramic method. The initial permeability is reduced in both citrate method as compared to the normal ceramic methods. However, with sintering temperature the initial permeability increases. The dielectric constant is reduced by the citrate method as compared to normal ceramic methods. These observations are explained on the basis of various mechanisms and models.

Powder X-ray diffraction, Raman scattering and infrared spectra at different doping (x = 0 ~ 0.5) on polycrystalline Pr_1-xSr_1+xCoO₄ were performed. With increasing x, the shift of Raman scattering spectra is due to the enhancement of electron–phonon interaction along the c-axis. The contrary variation of infrared in wavenumber comes from the weakening electron–phonon interactions in the ab plane. There is a dramatic variation in resistivity as x increases, which is also caused by increasing carrier concentration and is related to the band shift. For Pr_1-xSr_1+xCoO₄, both A_1g bands shift to low frequency and reach a minimum when x = 0.3 and the resistivity of Pr_0.7Sr_1.3CoO₄ is the smallest at room temperature.

The co-doping effect of Zn and Pr impurities in the compounds of composition Y_1-xPr_xBa₂[Cu_1-yZn_y]₃O_7-δ with x = 0.1, x = 0.2 and 0 ≤ y ≤ 0.1 has been investigated by analyzing the results of electrical resistivity measurements. It is found that for Pr substitution at x = 0.1, there is a minimal influence on in-plane processes, thereby slightly affecting T_c and residual resistivity ρ₀, but with the resistivity slope dρ/dT becoming large for the range of y from 0.03 to 0.06, leading to a larger depinning effect. For x = 0.2 a drastic change is observed whereby ρ₀ becomes abnormally large, and dρ/dT becomes negative, implying totally pinned charge stripes and no depinning. This second observation therefore suggests that Pr substitution converts the overdoped system to an optimally doped system, leading to the universal superconductor–insulator transition.

The transport of electrons through TiO₂ anatase and rutile thin films synthesized via sol–gel route has been investigated using electronic and optical spectroscopic studies. Mesoporosity of the films is confirmed by poroellipsometry. A smaller electron effective mass in anatase can be accounted for larger effective Bohr radius of trap electrons observed in anatase than in rutile. Further, the smaller effective mass in anatase favors high mobility. A mott transition is observed in anatase with change in temperature but not in rutile. Luminescence of self-trapped excitons is observed in anatase thin films, that implies a strong lattice relaxation.

Azimuthal electromagnetic wave logging-while-drilling (LWD) technology can detect weak electromagnetic wave signal and realize real-time resistivity imaging. It has great values to reduce drilling cost and increase drilling rate. In this paper, self-adaptive hp finite element method (FEM) has been used to study the azimuthal resistivity LWD responses in different conditions. Numerical simulation results show that amplitude attenuation and phase shift of directional electromagnetic wave signals are closely related to induced magnetic field and azimuthal angle. The peak value and polarity of geological guidance signals can be used to distinguish reservoir interface and achieve real-time geosteering drilling. Numerical simulation results also show the accuracy of the self-adaptive hp FEM and provide physical interpretation of peak value and polarity of the geological guidance signals.

Thin films ${\mathrm{\text{Mn}}}_{1.5}{\mathrm{\text{Co}}}_1{\mathrm{\text{Ni}}}_{0.5}{\mathrm{\text{O}}}_4$ (MCNO), ${\mathrm{\text{Mn}}}_{1.5}{\mathrm{\text{Co}}}_1{\mathrm{\text{Ni}}}_{0.35}{\mathrm{\text{Cu}}}_{0.15}{\mathrm{\text{O}}}_4$ (MCNCuO) and ${\mathrm{\text{Mn}}}_{1.5}{\mathrm{\text{Co}}}_1{\mathrm{\text{Ni}}}_{0.2}{\mathrm{\text{Cu}}}_{0.15}{\mathrm{\text{Sc}}}_{0.15}{\mathrm{\text{O}}}_4$ (MCNCuScO) are prepared by Chemical Solution Deposition method. The results show that the addition of Cu and Cu/Sc elements can reduce the grain boundary energy and the grain boundary angle to improve the single crystal degree of MCNO thin film. Through the analysis of MCNCuScO thin film, it is found that the stability of spinel structure mainly depends on the octahedron rather than tetrahedron. The bandgap of the samples from small to large is separately MCNCuScO, MCNCuO and MCNO films. The absorptivity within the waveband of $\lambda \le 1.5\mu \mathrm{\text{m}}$ plays a decisive role in the performance of the detector. At the same frequency, the MCNCuO thin film detector has the highest voltage responsivity, followed by the MCNCuScO thin film detector, while the MCNO film detector has the lowest responsivity.