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Equimolar powder mixtures and multilayer pellets of single‐phase Sr‐doped lanthanum manganite perovskite materials Lay‐xSrxMnO3 with La content y = 1 and 0.95 and Sr content 0 ≤ x ≤ 0.5 were annealed in air with 8 mol% Y2O3‐ZrO2 at 1470 K, up to 400 h and at 1670 K. up to 200 h. X‐ray diffraction and electron probe microanalysis confirmed the formation of La2Zr2O7 or SrZrO3 depending on the composition of the perovskites. No reaction products could be detected for La0.95‐xSr xMnO3 with 0.2 ≤ x ≤ 0.4 after annealing for 400 h at 1470 K, and for the perovskite La0.65Sr0.3MnO3 even after annealing for 200 h at 1670 K. The results demonstrate the improved chemical compatibility of La‐deficient perovskites against reaction with zirconia and can provide a basis for the selection of a sufficiently chemically stable material for the air electrode of solid oxide fuel cells.

The low-temperature specific heat and electrical resistivity of the polycrystalline non-stoichiometric manganites La 0.95−x Sr x MnO 3 have been investigated in the doping region x = 0.00-0.30. The specific heat has terms proportional to T and T 3 . The resistivity of the samples decreases as T 1/2 with increasing temperature, goes through a minimum and then increases proportionally to T 3 . The temperature T min , corresponding to the minimum of the resistivity, shifts with Sr content as T min ∼ x −2/5 .

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The resistivity minimum in manganites is still under debate. Recent publications discussed two possible scenarios: (i) electron–electron interaction in weak disordered systems and (ii) charge carriers tunnelling between antiferromagnetic coupled grains. In order to resolve this puzzle, we present a systematic study on the electrical resistivity, ρ(T), which was carried out in ceramic samples of La0.75Sr0.20MnO3 and La0.75Sr0.20Mn1−cCocO3 manganites over the temperature ranges 0.4–60 K and 4–60 K respectively. All compounds show a minimum in the resistivity at a characteristic temperature Tmin, which in the Co-doped samples shifts towards higher temperatures as the Co concentration increases. Tmin varies approximately as c1/3. The application of an external magnetic field shows that the Tmin decreases linearly as the field increases, and above 0.7 T remains field independent. In magnetic fields, where Tmin is constant, Tmin varies as . For temperatures below Tmin the resistivity data can be fitted either with a or with a −lnT function, while for temperatures above the minimum the resistivity follows both a T3 and a T5/2 dependence. We believe that there is a crossover between a ‘Kondo-like’ scattering process and the 3D electron–electron interaction effects enhanced by disorder.

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Strontium‐doped lanthanum manganite powders were prepared using a peroxide acetate salt based solution. The stable sol was peptized by reacting ammonium hydroxide with the precursor solution. The amorphous dried gel powders exhibit a high energy level, due to their high cations coordination and small particles, to develop the perovskite phase. This crystalline phase development from powders containing monocarboxylate ligands was characterized by thermal analysis (TG, DTG, DTA), X‐ray diffraction, and IR spectroscopy. The transformation from amorphous powders into a crystallized homogeneous oxycarbonate phase in a first stage corresponds to an exothermal DTA peak at 270°C. X‐ray diffraction patterns and IR spectra showed similar behavior of the powders after complete organic removal, during the conversion into perovskite phase starting at approximately 630°C and achieved about 700°C and achieved about 700°C, as well as during the sintering process.

We have created extremely small and independent Bose systems by confining "^He in bubbles of radius of less than 110 A in Cu foils. The size distribution and density of the bubbles were adjusted by annealing the samples and were determined by transmission electron microscopy. At low temperatures the confined helium becomes first solid, then liquid, and eventually superfluid as the mean bubble size is increased by annealing. The modification of superfluidity in this new confining geometry by size effects has been investigated by low-temperature calorimetry.PACS numbers: 64.70.Dv, 65.20.+w, 67.40.Kh, 67.70.+ n Because of its purity and homogeneity, liquid helium is a unique system for studies of finite-size effects. The superfluid transition of helium has been investigation in various confining geometries, e.g., helium films on planar substrates, and helium in Vycor glass, Nuclepore filters, or fine powders. Observed modifications of superfluidity were in qualitative agreement with expectations of the mean-field theory and were also compared to finite-size scaling arguments. Experimental data could not, however, always be used to test theoretical predictions because of insufficient knowledge and of complexity of the confining system. In the case of porous materials an additional disadvantage is the connectivity of the pores, which may reduce the effectiveness of the confinement.Following a different approach we have confined high-pressure helium gas in nonconnected cavities (bubbles) in Cu. At low temperatures the confined helium liquifies. Here we report our results on lowtemperature calorimetry, particularly the effects of pore size on the superfluid transition in bubbles of average radius between 25 and 108 A. Low-temperature calorimetrie evidence for superfluidity of helium in voids in irradiated solids has previously been reported by Keesom and co-workers,^ Aslanian and Weil,^ and Gmelin^; indications for size effects can be inferred from the data in Ref. 2.This new confining geometry is well defined and is topologically simple as we show by transmission electron microscopy (TEM). It creates an ensemble of extremely small Bose systems completely isolated from each other and consisting of about 10^ helium atoms each. Our work presents, in addition, experimental thermodynamic support for the properties of helium in small bubbles in a metal.Helium is practically insoluble in metals.^ Therefore, when helium is injected or produced in a metal it precipitates into microscopic bubbles whose size can be increased by annealing of the specimens. Significant reemission of helium from bulk metallic specimens charged with low helium concentrations is observed only in the neighborhood of the melting temperature of the metal. The gas pressure in the bubbles is in the kilobar range so that its density can be very high.'^^^ According to the equation of state,^ liquid helium is expected to exist in Cu in bubbles of radius r > 40 A at low temperatures.We have introduced helium into 99.999%-pure Cu disks of 7-mm diam x 100-/xm th...