This review article focuses on the sol-gel preparation of high temperature superconducting oxides wherein different classes of gel technologies were utilized. These involve: 1) the sol-gel route based upon hydrolysis-condensation of metal-alkoxides, 2) the gelation route based upon concentration of aqueous solutions involving metal-chelates, often called as “chelate gel” or “amorphous chelate” route, and 3) the organic polymeric gel route. This paper reviews the current status of these sol-gel processes, and illustrates the underlying chemistry involved in each sol-gel technology. It is demonstrated that the chemical homogeneity of the gel is often disturbed by the differences in the chemistries of the cations. Prior to gelation the starting precursor solution containing various forms of metal-complexes must be chemically modified to overcome this problem. Illustration of a variety of strategies for success in obtaining a homogeneous multicomponent gel with no precipitation is focal point of this review article.

Invited review “sol-gel” preparation of high temperature superconducting oxides

There has been a resurgence of complex oxides of late owing to their ferroelectric and ferromagnetic properties. Although these properties had been recognized decades ago, the renewed interest stems from modern deposition techniques that can produce high quality materials and attractive proposed device concepts. In addition to their use on their own, the interest is building on the use of these materials in a stack also. Ferroelectrics are dielectric materials that have spontaneous polarization in certain temperature range and show nonlinear polarization–electric field dependence called a hysteresis loop. The outstanding properties of the ferroelectrics are due to non-centro-symmetric crystal structure resulting from slight distortion of the cubic perovskite structure. The ferroelectric materials are ferroelastic also in that a change in shape results in a change in the electric polarization (thus electric field) developed in the crystal and vice versa. Therefore they can be used to transform acoustic wav...

Processing, Structure, Properties, and Applications of PZT Thin Films

Preparation of nanoparticles of silver halides, superconductors and magnetic materials using water-in-oil microemulsions as nano-reactors

Solid oxide fuel cells (SOFCs) are complex electrochemical devices that offer significant advantages over conventional power generation technologies. Many of these advantages surround the environmental impact of energy generation and in particular the efficiency of power production coupled with the potential range of fuel sources that can be foreseen. Despite these advantages there remain a number of challenges that may delay the full commercialisation of the solid oxide fuel cell. Several of these surround the materials selection, function and interactions with other cell components. It is the intention of this article to highlight the contribution that materials chemistry has made to the development of SOFCs and the future progress that is dependent on advances in materials chemistry.

Solid oxide fuel cells - a challenge for materials chemists?

Optical properties and electrochromic characterization of sol–gel deposited ceria films

Magnetic Shielding Analysis of Axisymmetric HTS Plates in Mixed State

The magnetic shielding effect of Ba2YCu3O7-δ, Cu and Fe-Ni plates was examined as a function of the frequency of applied ac magnetic field using magnetic heads. The effect of Ba2YCu3O7-δ plates was superior to that of Cu and Fe-Ni plates in the low-frequency ( 10 kHz) region, the effect of Ba2YCu3O7-δ plates was almost the same or slightly inferior to that of Cu plates. The shielding effect of Ba2YCu3O7-δ plates was strongly affected by the micro cracks and porosity of the samples. The magnetic shielding effect of Ba2YCu3O7-δ plates decreased rapidly with applied dc magnetic field, while the effect of Cu and Fe-Ni plates did not change with the application of dc magnetic field.

https://iopscience.iop.org/article/10.1143/JJAP.29.2403/pdf

Magnetic Shielding Effect of Ba2YCu3O7-δ Plates

We have investigated the effect of the deposition rate, as a direct function of the laser pulse repetition rate, on the surface morphology of CeO2 films deposited by the pulsed laser deposition (PLD) technique on r-cut Al2O3 (1102) substrates. The critical thickness is defined as the thickness before the onset of increased growth of large islands and abrupt increase in surface roughening. Two regimes of growth were found within the investigated range of deposition rate. It is found out that in the high deposition rate-regime (within 2–4 nm/min), the critical thickness is ∼90 nm, but in the low deposition rate-regime (less than 1 nm/min), the critical thickness is shifted to ∼40 nm. Films belonging to these two regimes of crystalline growth were found to have characteristically different formations and surface morphologies. As observed through atomic force microscopy (AFM), the surface morphology is composed of longitudinal islands forming a maze-like pattern in the high deposition rate-regime, while the characteristic morphology was composed of rounded islands in the low deposition rate-regime. Significant reduction in the areal density of large islands and characteristically smoother films was achieved using a low deposition rate.

Effect of deposition rate on the surface morphology of CeO2 films deposited by pulsed laser deposition

The Ba1-xLnxCuO3-y compounds (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Yb) with x=0.34 and (Ln=Nd, Sm and Eu) with x=0.2, 0.4 and 0.5 were prepared. A superconducting transition between 75 and 93 K was observed magnetically in the compounds (Ln=Nd, Sm, Eu, Ho and Er) with x=0.34. X-ray studies showed that most compounds with high Tc have the oxygen-defect perovskite structure.

Shigetoshi Ohshima

Papers

Magnetic Shielding Analysis of Axisymmetric HTS Plates in Mixed State

Magnetic Shielding Effect of Ba2YCu3O7-δ Plates

Effect of deposition rate on the surface morphology of CeO2 films deposited by pulsed laser deposition

Superconducting and Structural Properties of the New Ba1-xLnxCuO3-yCompound System (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Yb)

In-plane orientation of C-axis oriented YBa2Cu3Ox films on MgO substrates