Highly ordered BiFeO3（BFO） nanotubes with about 200nm in diameter and 60μm in length are fabricated by a sol-gel AAO template method. A perovskite-type structure of BFO is confirmed in the nanotubes by transmission...Highly ordered BiFeO3（BFO） nanotubes with about 200nm in diameter and 60μm in length are fabricated by a sol-gel AAO template method. A perovskite-type structure of BFO is confirmed in the nanotubes by transmission electron microscopy and selected area electron diffraction analysis. The coexistence of ferroelectric and ferromagnetic ordering of these BFO nanotubes at room temperature is demonstrated, giving a remnant polarization of 26μC/cm2, a low coercive electric field of 60kV/cm, and a magnetization of 0.18emu/g. In addition, it is found that the leakage behavior of these nanotubes is dominated by the ohmic contact mechanism.展开更多
The Zn2＋, Ni2＋ and Co3＋ doped Sr14Cu24041 compounds were synthesized by standard solid state method. X-ray diffraction results show that the changes in lattice parameters are very small. Selected area electron diff...The Zn2＋, Ni2＋ and Co3＋ doped Sr14Cu24041 compounds were synthesized by standard solid state method. X-ray diffraction results show that the changes in lattice parameters are very small. Selected area electron diffraction patterns （EDPs） show that the diffraction spots corresponding to the CuO2 chain substructure are extended to streaks along a＊ and b＊ directions for all the samples, while the diffraction spots produced merely by the Cu203 ladder substructure are still very sharp. This means that the periodicities of chains in a＊ and b＊ directions are partially destroyed upon doping ofZn, Ni and Co due to that the initial phase of each chain becomes a random variable. The temperature dependence of magnetic properties was measured for every sample. And the number of dimers in CuO2 chain per formula unit （f.u.） and dimer coupling constant are obtained by fitting the temperature dependence of the magnetic susceptibility. It is found that the degree of initial phase disorder is related to the order degree of magnetic sequence in CuO2 chain. For the un-doped sample, the decoupling of dimers is weak, the magnetic sequence is slightly destroyed, and the streaks in EDP are also very weak, which implies the degree of initial phase disorder in CuO2 chain is very low. When Zn2~ and Ni2＋ ions are doped, the number of dimers per f.u. decreases, and the intensity of diffraction streaks increases in comparison with the corresponding spots. Furthermore, when the high spin magnetic ions Co3＋ are doped, the number of holes in Sr14Cu24041 decreases, the magnetic sequence is destroyed very seriously, and the spots in EDP are extended to streaks almost completely. The phenomenon that the diffraction spots ofCuO2 chain extend to streaks in EDP appears as evidence that the magnetic sequence in the CuO2 chain is destroyed by doping of Zn, Ni, Co.展开更多
Nd doped multiferroic BiFeO3 (Bi0.94Nd0.06FeO3 (BNF)) nanotubes were successfully synthesized by a sol-gel template method.Electron microscopy investigations exhibited that these nanotubes had straight and smooth prof...Nd doped multiferroic BiFeO3 (Bi0.94Nd0.06FeO3 (BNF)) nanotubes were successfully synthesized by a sol-gel template method.Electron microscopy investigations exhibited that these nanotubes had straight and smooth profile with diameters of about 200 nm and wall thickness of about 20 nm.A perovskite-type structure of BNF was confirmed in the nanotubes by high-resolution transmission electron microscopy and selected area electron diffraction analysis.These nanotubes had high resistivity.The dielectric constant and dielectric loss of the nanotubes were 126 and 0.040 at 1 MHz, respectively.The ferroelectric properties of these BNF nanotubes were demonstrated with a remnant polarization of 48 μC/cm2 and a coercive electric field of 163 kV/cm.展开更多
基金Supported by the National Basic Research Program of China under Grant No 2006CB932305 and the National Natural Science Foundation of China under Grant No 50872097.
文摘Highly ordered BiFeO3（BFO） nanotubes with about 200nm in diameter and 60μm in length are fabricated by a sol-gel AAO template method. A perovskite-type structure of BFO is confirmed in the nanotubes by transmission electron microscopy and selected area electron diffraction analysis. The coexistence of ferroelectric and ferromagnetic ordering of these BFO nanotubes at room temperature is demonstrated, giving a remnant polarization of 26μC/cm2, a low coercive electric field of 60kV/cm, and a magnetization of 0.18emu/g. In addition, it is found that the leakage behavior of these nanotubes is dominated by the ohmic contact mechanism.
基金Funded by the National Natural Science Foundation of China(Nos.10674105 and 50471028)
文摘The Zn2＋, Ni2＋ and Co3＋ doped Sr14Cu24041 compounds were synthesized by standard solid state method. X-ray diffraction results show that the changes in lattice parameters are very small. Selected area electron diffraction patterns （EDPs） show that the diffraction spots corresponding to the CuO2 chain substructure are extended to streaks along a＊ and b＊ directions for all the samples, while the diffraction spots produced merely by the Cu203 ladder substructure are still very sharp. This means that the periodicities of chains in a＊ and b＊ directions are partially destroyed upon doping ofZn, Ni and Co due to that the initial phase of each chain becomes a random variable. The temperature dependence of magnetic properties was measured for every sample. And the number of dimers in CuO2 chain per formula unit （f.u.） and dimer coupling constant are obtained by fitting the temperature dependence of the magnetic susceptibility. It is found that the degree of initial phase disorder is related to the order degree of magnetic sequence in CuO2 chain. For the un-doped sample, the decoupling of dimers is weak, the magnetic sequence is slightly destroyed, and the streaks in EDP are also very weak, which implies the degree of initial phase disorder in CuO2 chain is very low. When Zn2~ and Ni2＋ ions are doped, the number of dimers per f.u. decreases, and the intensity of diffraction streaks increases in comparison with the corresponding spots. Furthermore, when the high spin magnetic ions Co3＋ are doped, the number of holes in Sr14Cu24041 decreases, the magnetic sequence is destroyed very seriously, and the spots in EDP are extended to streaks almost completely. The phenomenon that the diffraction spots ofCuO2 chain extend to streaks in EDP appears as evidence that the magnetic sequence in the CuO2 chain is destroyed by doping of Zn, Ni, Co.
基金supported by the National Basic Research Program of China (2006CB932305)National Natural Science Foundation of China (50872097)
文摘Nd doped multiferroic BiFeO3 (Bi0.94Nd0.06FeO3 (BNF)) nanotubes were successfully synthesized by a sol-gel template method.Electron microscopy investigations exhibited that these nanotubes had straight and smooth profile with diameters of about 200 nm and wall thickness of about 20 nm.A perovskite-type structure of BNF was confirmed in the nanotubes by high-resolution transmission electron microscopy and selected area electron diffraction analysis.These nanotubes had high resistivity.The dielectric constant and dielectric loss of the nanotubes were 126 and 0.040 at 1 MHz, respectively.The ferroelectric properties of these BNF nanotubes were demonstrated with a remnant polarization of 48 μC/cm2 and a coercive electric field of 163 kV/cm.
