Mn site substitution of La0.67Ca0.33MnO3 with closed shell ions: Effect on magnetic transition temperature

Mn site is substituted with closed shell ions (Al, Ga, Ti, Zr and a certain combination of Zr and Al) and also with Fe and Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at %. Substitution did not change either the crystal symmetry or the oxygen stoichiometry. All substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures (T _p(ρ) and T _C, respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising due to difference in the ionic radii between the substituent (r _M) and the Mn³⁺ ion (r _Mn ³⁺) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and that of the neighboring Mn ion.     

DSC analysis of Cu–Zn–Sn shape memory alloy fabricated via electrodeposition route

Cu–Zn–Sn shape memory alloy strips with composition range of 13.70–46.30 mass% Sn were fabricated by electrodepositing Sn on a shim brass surface and then subsequently annealed at a constant temperature of 400 °C for 120 min under flowing nitrogen. Subjecting the Sn-plated strips to differential scanning calorimetry (DSC) analysis revealed that the austenitic start (A _s) temperature was essentially constant at 225 °C while the martensite start (M _s) temperature was consistently within the 221.5–222 °C interval. Austenite to martensite phase transformation showed two distinct peaks on the DSC thermogram which can be attributed to the non-homogeneity of the bulk Cu–Zn–Sn ternary alloy. The latent heats of cooling and heating were found to increase with the mass% Sn plated on the shim brass. Effect of annealing temperature was also investigated wherein strips with an essentially constant composition of 26 mass% Sn were annealed at a temperature range of 350–420 °C for 120 min under flowing nitrogen. Varying the annealing temperature has no significant effect on the transformation temperatures of the ternary alloy.     

Performance of perovskite-related oxide cathodes in contact with lanthanum silicate electrolyte

The cathodic performance of selected mixed-conducting electrodes, including perovskite-type SrMn_0.6Nb_0.4O_3 ? δ, Sr_0.7Ce_0.3Mn_0.9Cr_0.1O_3 ? δ and Gd_0.6Ca_0.4Mn_0.9Ni_0.1O_3 ? δ, and Ruddlesden–Popper La₂Ni_0.5Cu_0.5O_4 + δ, LaSr₂Mn_1.6Ni_0.4O_7 ? δ, La₄Ni_3 ? xCu_xO_10 ? δ (x = 0–0.1) and La_3.95Sr_0.05Ni₂CoO_10 ? δ, was evaluated in contact with apatite-type La₁₀Si₅AlO_26.5 solid electrolyte at 873–1073 K and atmospheric oxygen pressure. The electrochemical activity of porous nickelate-based layers was found to correlate with the concentration of mobile ionic charge carriers and bulk oxygen transport, thus lowering in the series La₄Ni_2.9Cu_0.1O_10 ? δ > La₄Ni₃O_10 ? δ > La_3.95Sr_0.05Ni₂CoO_10 ? δ and decreasing on copper doping in K₂NiF₄-type La₂Ni_1 ? xCu_xO_4 ? δ. The relatively high overpotentials of nickelate-based cathodes, varying in the range ? 240 to ? 370 mV at 1073 K and current density of ? 200 mA/cm², are primarily associated with surface diffusion of silica from La₁₀Si₅AlO_26.5, which partially blocks the electrochemical reaction zone. As compared to the intergrowth nickelate materials, the manganite-based electrodes exhibit substantially worse electrochemical properties, in correlation with the level of oxygen-ionic and electronic conduction in Mn-containing phases. The effects of cation interdiffusion between the cell components as a performance-deteriorating factor are briefly discussed.     

Experimental evidence of time-delay-induced death in coupled limit-cycle oscillators

Experimental observations of time-delay-induced amplitude death in two coupled nonlinear electronic circuits that are individually capable of exhibiting limit-cycle oscillations are described. The existence of multiply connected death islands in the parameter space of coupling strength and time delay for coupled identical oscillators is established. The existence of such regions was predicted earlier on theoretical grounds [Phys. Rev. Lett. 80, 5109 (1998); Physica (Amsterdam) 129D, 15 (1999)]. The experiments also reveal the occurrence of multiple frequency states, frequency suppression of oscillations with increased time delay, and the onset of both in-phase and antiphase collective oscillations.     

Autosoliton model of the spinning fronts of reaction

Experiments with reaction fronts (detonation waves and solidflames) reveal that, near the combustion limit, the fronts movein a spinning regime when localized zones of intensive reactiontravel along spiral trajectories. In the paper, the spinningwave is interpreted as an autosoliton and described phenomenologicallyby a nonlinear partial differential equation. The equation isstudied numerically, and the presence of the stable spinningand autosoliton solutions is shown.