Cu-doping induced ferromagnetic insulating behavior and domain wall pinning effects in LaMnO_3

A systematic study on the structural, magnetic, and electrical transport properties was performed for the LaMnlxCUxO3 system. A single phase of orthorhornbic perovskite structure was formed for x = 0.05-0.40. A striking paramagnetic-ferromagnetic transition and a considerable magnetoresistance effect were observed at the ferromagnetic ordering temperature Tc, but no insulator-metal transition induced by Cu-doping was observed. Below Tc, a visible unexpected drop was observed in the ac susceptibility and zero-field-cooled dc magnetization for the dilute doped samples with x≤0.10, which was proven to be associated with domain wall pinning effects by milling the bulk material into single domain particles. It is validated that there is no exchange interaction between Cu and Mn, and double exchange interactions between Mn^3＋ and Mn^4＋ are induced by Cu-doping in the anti-ferromagnetic LaMnO3 matrix, whereas the severe distortion and disorder caused by occupied-dopant prohibits charge carriers from hopping.

Synthesis of La-hexaaluminate catalyst for methane combustion by a reverse SDS microemulsion

La-hexaaluminate catalyst for methane catalytic combustion was synthesized by a reverse microemulsion. Pseudo-temary phase diagrams of a quaternary microemulsion system of sodium dodecyl sulfate （SDS）, n-pentanol, n-octane, and water （or Al（NO3）3 solution） were presented. The effects of alcohol chain length, cosurfactant-to-surfaqtant rat!0, and salt concentration on the formation and stability of the microemul- sion system were studied. The phenomenon that the conductivity changed with water supported the phase behavior of the microemulsion system. La（MnffFex）Al12_xO19_a catalysts, applied in methane combustion and with high-temperature stability, were synthesized within the stable areas of the phase diagram of the microemulsion system, when SDS was chosen as surfactant, n-pentanol as cosurfactant, and n-octane as oil phase. The physical properties and structure of the catalysts were characterized by BET method, transmission electron microscope （TEM）, and X-ray diffraction （XRD）. A micro-fixed-bed reactor was used to measure the catalytic activity of hexaaluminates in methane combustion. The results show that the reverse microemulsions can be used to produce discrete La-hexaaluminate nanoparticles that display excellent methane combustion activity owing to their high surface area and high thermal stability.

Study of Metal-Oxygen Vibrations in Rare Earth o-Chlorobenzoates

The far-IR spectra of ML3&middotH2O (M=Y, La-Lu; HL=o-chlorobenzoic acid) have been studied, and the wavenumbers of M-O vibrations (νM-O) have been assigned. It is found that ν-O increases as the atomic number of lanthanide element increase. Moreover, the plot of νM-O-L (L is the total orbital angular quantum number of lanthanide ion in ground state) shows an inclined W systematics.

Characteristics of a PLZT electro-optical deflector

A beam deflector was designed and fabricated by using a lead lanthanum zirconate titanate （PLZT） ceramic with high quadratic electro-optic （EO） effect, based on refraction at an interface between areas with and without applied voltage. Its EO coefficients of R33 = 2.1×10^-16 V^2/m^2 and R13 = -0.37×10^-16 V^2/m^2 were obtained. Moreover, the hysteresis characteristics of the EO deflection were observed, and the effects of temperature on the characteristics of beam deflector were also investigated in detail.