Narrow Results

Pb_0.76-3x/2La_xCa_0.24Mn_0.02Ti_0.98O₃ (PLCT), x=0–0.08 (in steps of 0.02), ceramics were prepared by conventional mixed oxide technique. The samples were sintered at an optimized temperature of 1150°C. Phase and microstructural analysis were carried out using X-ray Diffraction (XRD) and scanning electron microscope (SEM) to study the effect of lanthanum on PCT ceramics. Both experimental and theoretical densities for all the samples were also determined. Phase analysis shows the single-phase material with tetragonal structure and the decrease in tetragonality is observed with the increase in the amount of lanthanum in the base composition. Detailed dilatometric investigations were performed in order to study the shrinkage behaviour and dominating shrinkage mechanism in the present system.

The oxidation of Ti₁₉Al₁₈La₄N₅₇ coating was studied at 600°C, 700°C, and 800°C for up to 30 h in air. The coating consisted of fine Ti₃Al₃N₂ polycrystals. The oxides formed were an amorphous mixture of Al₂O₃, TiO₂, and La₂O₃. During oxidation, nitrogen diffused out from the coating. The addition of 4 at.%La to the TiAlN coating deteriorated the soundness of the oxide film formed.

This work describes the synthesis, analysis, and testing of the novel type of La/graphene composites as potential contrasting agents (CAs) for photon-counting computed tomography (PCCT). The impregnation of oxidized graphene nanoflakes (GNFs) with Lanthanum nitrate solution resulted in uniform distribution of La-containing particles on the flake surface with particle size of about 2–3 nm. La was confirmed to be a suitable contrasting element for PCCT that could be visualized in reference phantom media and in the presence of other CAs. Minimum concentration of La in the composites determined by PCCT was in the range of 2.5–5 mg⋅ml${}^{-1}$.

La_2−xSr_xNiO₄ shows a maximum in the c/a ratio around x = 0.6 up to which composition the concentration of holes is equal to that expected theoretically. The material becomes a degenerate semiconductor above a certain temperature up to x = 0.8, but is metallic at room temperature when x ≥ 1.0. All the compositions with x ≥ 0.05 are paramagnetic in the 15 - 300K range. Based on these measurements, an electronic phase diagram is tentatively proposed. It is noteworthy that the antiferromagnetic order disappears at low doping levels in both La_2−xSr_xNiO₄ and La_2−xSr_xCuO₄, but metallicity is seen at 300K only at a much higher x value in the former system.