High-performance oxygen permeation membranes:Cobalt-free Ba_(0.975)La_(0.025)Fe_(1-x)Cu_(x)O_(3)-δceramics

A new group of cobalt-free perovskite oxides,Ba_(0.975)La_(0.025)Fe_(1-x)Cu_(x)O_(3-δ)(BLFC,x=0.05-0.15),was designed,characterized and applied as oxygen permeation membranes.It was found that BLFC oxides with Cu doping range of 0.075-0.15 maintain cubic perovskite phase in a wide range of temperatures.More Cu introduced at the B-site results in a gradual increase of the electrical conductivity,which is attributed to the denser overlapping of electron clouds of CueO bonds.With increasing Cu content,the oxygen vacancy concentration increases and the oxygen ion migration energy decreases,leading to the highest oxygen permeation flux of 1.59 mL cm^(-2)min^(-1)recorded for Ba_(0.975)La_(0.025)Fe_(0.9)Cu_(0.1)O_(3-δ)1mm thick membrane at 950℃.However,the oxygen permeability decreases with further Cu doping,which may be correspond to a presence of defect association.Ba_(0.975)La_(0.025)Fe_(0.9)Cu_(0.10)O_(3-δ)membrane with 0.7mm thickness delivers stable oxygen permeation flux of 1.57 mL cm^(-2)min^(-1)for 200 h at 900℃.All of the obtained results indicate that the developed BLFC with optimized Cu content(i.e.x=0.1)is a very promising material for usage in oxygen separation applications.

High-temperature ferromagnetic metallic phase in LaMnO_(3)/Sr_(3)Al_(2)O_(6)heterostructure

To achieve a flexible single-crystal multifunctional membrane,the freestanding process of a rigid epitaxial transition metal oxide thin film via a buffered water-dissolution sacrificial layer has attracted reasonable attentions.Owing to the difference in chemical potential,specific element affinity,and lattice constant between the target membrane and the sacrificial layer,the freestanding process may cause an indelible change of physics property once the target thin film is sensitive to the above factors.Here,the heterostructures composed of the generally adopted sacrificial layer Sr_(3)Al_(2)O_(6)(SAO)and LaMnO_(3)(LMO)have been systematically investigated.The electrical and magnetic properties of LMO show extreme sensitivity to the thickness of SAO(tSAO).Then we have also found that LMO/SAO heterostructures can exhibit the coexistence of two ferromagnetic phases,the significantly enhanced Curie temperature~342 K,and the large magnetoresistance-23.3%at 300 K,which is similar to the optimal-doped manganite such as La_(2/3)Sr_(1/3)MnO_(3).X-ray diffraction results show that continuously tunable strain from out-of-plane tension to relaxation and then to compression can be generated by adjusting tSAO.This strain can stabilize the migrated oxygen from LMO to SAO,which is induced by the large oxygen affinity difference between Bsite Mn and Al.It is believed that these unexpected electrical/magnetic phenomena are originated from the combined effects of interfacial element diffusion and strain.Our study provides a strategy for designing new magnetic phases,and a reference for the fundamental understanding of strongly correlated transition metal oxide systems in the freestanding process.