How to improve the specific power density of the rechargeable lithium ion battery has recently become one of the most attractive topics of both scientific and industrial interests. The spinel LiMn2O4 is the most promising candidate as a cathode material because of its low cost and nontoxicity compared with commercial LiCoO2. Moreover, nanostructured electrodes have been widely investigated to satisfy such industrial needs. However, the high-temperature sintering process, which is necessary for high-performance cathode materials based on high-quality crystals, leads the large grain size and aggregation of the nanoparticles which gives poor lithium ion battery performance. So there is still a challenge to synthesize a high-quality single-crystal nanostructured electrode. Among all of the nanostructures, a single crystalline nanowire is the most attractive morphology because the nonwoven fabric morphology constructed by the single crystalline nanowire suppresses the aggregation and grain growth at high temperature, and the potential barrier among the nanosize grains can be ignored. However, the reported single crystalline nanowire is almost the metal oxide with an anisotropic crystal structure because the cubic crystal structure such as LiMn2O4 cannot easily grow in the one-dimentional direction. Here we synthesized high-quality single crystalline cubic spinel LiMn2O4 nanowires based on a novel reaction method using Na0.44MnO2 nanowires as a self-template. These single crystalline spinel LiMn2O4 nanowires show high thermal stability because the nanowire structure is maintained after heating to 800 degrees C for 12 h and excellent performance at high rate charge-discharge, such as 20 A/g, with both a relative flat charge-discharge plateau and excellent cycle stability.
Ultrasound is used as an external trigger for the pulsatile release of the drug ibuprofen. The system is composed of mesoporous silica as the drug reservoir and poly(dimethylsiloxane) (PDMS) as an implantable body. This system could find use for in vivo delivery of drugs in response to changes in physiological conditions.
A triaxial LiFePO4 nanowire with a multi wall carbon nanotube (VGCF:Vapor-grown carbon fiber) core column and an outer shell of amorphous carbon was successfully synthesized through the electrospinning method. The carbon nanotube core oriented in the direction of the wire played an important role in the conduction of electrons during the charge-discharge process, whereas the outer amorphous carbon shell suppressed the oxidation of Fe2+. An electrode with uniformly dispersed carbon and active materials was easily fabricated via a single process by heating after the electrospinning method is applied. Mossbauer spectroscopy for the nanowire showed a broadening of the line width, indicating a disordered coordination environment of the Fe ion near the surface. The electrospinning method was proven to be suitable for the fabrication of a triaxial nanostructure.
Epitaxial Pb(Zr,Ti)O3(PZT) films, 1.5–2.0μm in thickness, with a Zr∕(Zr+Ti) ratio ranging from 0.20 to 0.75 were grown on (100)c-,(110)c-, and (111)c-oriented SrRuO3∕∕SrTiO3 substrates at 600 °C by metal-organic chemical vapor deposition (MOCVD). The effects the Zr∕(Zr+Ti) ratio had on the crystal structure, dielectric and ferroelectric properties, and piezoelectric response of these films with different crystal orientations were systematically investigated. We ascertained from x-ray-diffraction reciprocal-space-mapping analysis that (001)T-∕(100)T-∕(100)R-,(101)T-∕(110)T-∕(110)R-∕(101¯)R-, and (111)T-∕(111)R-∕(111¯)R-oriented films had epitaxially grown on the respective (100)c-,(110)c-, and (111)c-oriented SrRuO3∕∕SrTiO3 substrates. The constituent phase changed from a tetragonal single phase, a mixture phase of a tetragonal and rhombohedral, to a rhombohedral single phase with increasing Zr∕(Zr+Ti) ratio irrespective of the orientation of the substrates. However, the range of the Zr∕(Zr+Ti) ratio of the film with the mixture phase differed depending on crystal orientation. This suggests that the stress relaxation process applied from the substrates changed due to crystal orientation. The relative dielectric constant was maximum for films with the mixture phase regardless of the crystal orientation. Remanent polarization was also maximum for these films on the (111)cSrRuO3∕∕SrTiO3 substrates, while it was minimum on the (100)c- and (110)c-oriented SrRuO3∕∕SrTiO3 substrates. Films with two phases coexisting had larger electric-field-induced strain than films with a single tetragonal or rhombohedral phase for the (111)-oriented films, but there were no remarkable changes in the (100)- and (110)-oriented films. Small ac signal measurements suggested that domain-wall motions easily occurred in the (111)-oriented films with the mixture phase compared with other orientations. These results indicated that the larger field-induced strain of the (111)-oriented PZT films consisting of a mixture of tetragonal and rhombohedral phases largely contributed to extrinsic factors such as domain-wall motions and phase transformation due to the applied electric field.
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