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Perovskite CH3NH3PbI3 is an ionic crystal with suitable band gap and conductivity for optoelectronic applications. The sensitivity of the CH3NH3PbI3 crystal and its derivatives to chemical composition, film-forming process, and even moisture lead to difficulties in evaluating its electronic structure and redox behavior using electrochemical techniques. Nevertheless, full understanding of the electrochemical behavior of the perovskite crystal is certainly beneficial for tuning its redox properties and chemical stability, especially for device fabrication. We show that the band structure of CH3NH3PbI3 can be successfully evaluated based on electrochemical square wave voltammetry. The energy level of the bottom of the conduction band of the perovskite crystal was determined directly from the onset reduction potential with reference to the onset oxidation potential of ferrocene, and estimated to be −3.56 eV; the top of the valence band, at –5.07 eV, was determined indirectly after taking into consideration the bandgap, because the oxidation current of the iodide ions shields that corresponding to the valence band of the CH3NH3PbI3 crystal. The overlap of the oxidation currents from the iodide ions and the valence band of the crystal suggests that there are excess iodide ions in CH3NH3PbI3 not involved in the development of the valence band. In addition, the alternating current (AC) impedance spectra of CH3NH3PbI3 indicate that the iodide ions are not completely immobilized. These imply that the defects in the crystal are related to the iodide ions to a large extent. The electrochemistry of CH3NH3PbI3 in an organic electrolyte reveals its coupling degradation during the redox processes in square wave and cyclic voltammetry. The degradation reactions result from the reduction of lead ions and oxidation of iodide ions in the perovskite crystal. In electrochemical reduction, along with the reduction that occurs in the conduction band, the lead ions in the crystal are reduced to metallic lead, which introduces a phase change in the crystal, as revealed in cyclic voltammetry; the metallic lead can be re-oxidized electrochemically. In the case of electrochemical oxidation, the iodide ions, as well as the valence band of CH3NH3PbI3, lose electrons. The electrochemically generated iodine diffuses into the organic electrolyte gradually, which results in the loss of iodide ions in the crystal. Such loss of iodide ions continues during the cyclic redox reaction. Apparently, the electrochemical investigations on perovskite CH3NH3PbI3 show that the crystal is extremely reactive during the redox process; attention should be paid on controlling the excess iodide ions and the irreversible phase change resulting from the oxidation of lead ions. 相似文献
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The thermal behaviors of clusters [Ag3WS3Br](PPh3)3 and [Cu3WS3Br](PPh3)3 (PPh3=triphenyl phosphine) in a nitrogen atmosphere were studied under the non-isothermal conditions by simultaneous TG-DTG-DSC and EDS techniques. The results showed that the evolution of PPh3 generally proceeded before the release of the other moiety in one or two step-mode. The mechanisms, the kinetic and the thermodynamic parameters for decomposition of PPh3 of both clusters were determined and calculated by jointly using several methods, which showed that its evolution was controlled by Avrami-Erofeev equation. The results also showed that there was no new stable phase composed of W-Ag(Cu)-S-Br after release of organic moiety PPh3 and that CVD method was not applicable to their further processing. 相似文献
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有关NdCl_3·3ROH-AlEt_3催化体系的活性 总被引:1,自引:0,他引:1
<正> 我们曾指出,在NdCl_3·3ROH-AlEt_3体系中,醇的作用在于它的给电子性将会降低稀土离子的正电性,从而减弱Nd-Cl键的离子性,同时引起晶格的变化,使之有利于烷基化作用的发生,导致活性提高。本实验采用一种简便的方法证实了这种作用的发生。 这个方法所根据的原理是一般Ziegler-Natta型催化组分的熟知反应形式: 相似文献
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LaVO3和NdVO3的合成 总被引:1,自引:0,他引:1
以V2O3为起始原料,在氩气中合成了ABO3型稀土钒化合物,对加热前通氩气的时间,V2O3∶La2O3的配比等进行了探讨,得到了适宜的制备条件。首次报道了LnVO3(Ln=La,Nd)的热学性质,发现LaVO3具有吸附二氧化碳的特性。 相似文献
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Crystal of Yb3+-doped Ba3Gd(BO3)3 has been grown by the Czochralski method. The spectroscopic characterizations have been investigated at room temperature. The Yb3+:Ba3Gd(BO3)3 crystal exhibits broad absorption at 976nm with FWHM of 7nm and large overall spitting of 2F7/2 manifold (823cm-1). The absorption and emission cross sections are 5.09×10-21cm2 at 976nm and 0.97×10-21cm2 at 1040nm,respectively. The fluorescence lifetime is 2.84 ms. 相似文献