Multistep Accelerated Aging of Magnetic Field Sensors Based on Nanostructured La–Sr–Mn–O Thin Films
We present results of investigation of accelerated aging influence on electrical resistivity and magnetoresistance (MR) of nanostructured La–Sr–Mn–O films used for magnetic field sensors, which could be applied in advanced scientific and industrial devices. The 400-nm-thick manganite films were grown by metal organic chemical vapor deposition technique. To investigate the effectiveness of accelerated aging, the three methods were tested: 1) thermal treatment of the sensor samples at 100 °C temperature in Ar atmosphere when film surface was uncoated; 2) thermal treatment of the samples coated prior to treatment by polymer; and 3) multistep aging including both previous methods: thermal treatment of the samples with uncoated surface in Ar atmosphere and additional thermal treatment of the coated samples. The sensor samples were studied without and in pulsed magnetic field up to 20 T. To describe the underlying processes, the kinetics of resistivity change during accelerated aging was analyzed using a stretched exponent relaxation function. It was found that the best long-term stability of resistivity in time demonstrated samples treated by a multistep accelerated aging method. All three aging methods resulted in minor influence (<1%) on MR of the films in magnetic fields up to 20 T.
A SIMS study of oxygen tracer diffusion and surface exchange in La0.8Sr0.2MnO3+δ
Abstract The 18 O/ 16 O isotope exchange/depth profile (IEDP) method has been employed to investigate oxygen tracer diffusion and surface exchange behaviour in the perovskite oxide La 0.8 Sr 0.2 MnO 3+ δ at temperatures between 700°C and 1000°C. The activation enthalpy for oxygen tracer diffusion in the bulk ( D b *) was found to be 270±13 kJ mol −1 , while that for oxygen tracer surface exchange ( k s *) was 128±21 kJ mol −1 . Evidence of short circuit diffusion was observed in all 18 O penetration profiles, and this was ascribed to fast diffusion down grain boundaries. D b * and k s * were also determined as a function of oxygen partial pressure at 1000°C: D b *was found to vary according to P O 2 −0.41 ; the P O 2 dependence of k s *was unclear, as the 18 O penetration profiles at 1000°C were diffusion-limited.
Synthesis and chemical recycling of novel poly(ester-urethane)s using an enzyme.
A series of enzymatically recyclable poly(ester-urethane)s consisting of a biodegradable diurethane moiety as a hard segment and an ester moiety as an enzymatically cleavable linkage was chemo-enzymatically prepared by two routes. The poly(ester-urethane) was prepared by a) the ring-opening polymerization of a cyclic ester-urethane monomer synthesized via the transesterification reaction of biodegradable diurethanediol and dicarboxylate ester using lipase and b) the direct polycondensation of a diurethanediol and a dicarboxylate ester. A significantly higher molecular-weight poly(ester-urethane) having the highest molecular weight (Mw) of 101,000 was produced by the ring-opening polymerization of the cyclic ester-urethane monomer when compared with that produced by the polycondensation of the dicarboxylate ester with diurethanediol. The poly(ester-urethane) was readily degraded by lipase into the corresponding cyclic oligomers; the oligomers were readily repolymerized by the ring-opening polymerization using lipase for chemical recycling.