RESUMEN
Recently the layered oxide semiconductor Bi2O2Se was hotly explored for its ultrahigh mobility and ultrafast photo-response whose physical origins need to be further explored or elucidated. Here, we have grown halogen (Cl, Br, I) doped and un-doped Bi2O2Se single crystals by a melt-solidification method. Comparative electrical transport characterizations and detailed data-analysis substantiate that the electron-electron scattering is the major source of resistivity in un-doped Bi2O2Se crystals; however, in halogen-doped Bi2O2Se crystals, electron-electron scattering is only effective at low temperature (<60 K) and subsequently electron-phonon-interaction scattering is dominated to resistivity. Hall measurement and analysis show that electron concentration of halogen-doped Bi2O2Se (â¼1020 cm-3) is one-order higher than un-doped one (â¼1019 cm-3), but the carrier mobility of halogen-doped Bi2O2Se at 2 K (â¼102 cm2 V-1 s-1) is reduced by more than two orders than un-doped ones (â¼104 cm2 V-1 s-1). Three kinds of relaxation time (due to the impurity scattering, electron-electron scattering and electron-phonon scattering), calculated by linear-response theory and electron-/phonon-dispersion, are in agreement with experimental results quantitatively. The scattering mechanism evolution from sole electron-electron scattering (un-doped Bi2O2Se) to electron-phonon scattering (doped Bi2O2Se) at high temperature (>60 K) is attributed to the net effect of decreased screened Coulomb-interaction and increased Fermi energy in halogen-doped Bi2O2Se. This work may provide clues of physical origins of superior electrical/photoelectrical properties of Bi2O2Se.
RESUMEN
We obtained one new molecular ferroelectric material tris(2-hydroxyethyl) ammonium bromide (TAB) that crystallizes in aqueous solution at room temperature with a space group of R3m which belongs to ten polar space groups. There is a paraelectric-to-ferroelectric phase transition at 424 K (from hexagonal R3Ì m to hexagonal R3m phase). Such a high transition temperature is close to that of diisopropylamine bromide (426 K) and higher than that of many other molecular ferroelectrics, such as triethylmethylammonium tetrabromoferrate(III) (360 K); some of the organic-inorganic perovskite ferroelectrics, such as (cyclohexylammonium)2PbBr4 (363 K); and some inorganic ferroelectrics, including BaTiO3 (393 K). The saturated polarization and the coercive field of TAB measured from the ferroelectric hysteresis loop are about 0.54 µC·cm-2 and 0.62 kV/cm, respectively. Given its superior performance, including high phase transition temperature, room-temperature ferroelectricity, small coercive electric field, and adjustable ladder-shaped dielectric constant, TAB will have many potential applications.
RESUMEN
Hybrid organic-inorganic halide perovskites (HOIPs) MAPbBr3 and their ramifications have emerged because of the photovoltaic, optical, and other fascinating performances of HOIPs in recent years. However, many intrinsic properties, such as crystal structure and ferroelectricity, are still controversial. In this work, the ferroelectricity of the orthorhombic and tetragonal MAPbBr3 single crystal was confirmed through the dielectric behavior versus bias electric field ε( E), the temperature-dependent pyroelectric current with positive/negative poling, and the positive-up-negative-down (PUND) measurements. The electric field dependence of dielectric constant curves shows a butterfly type shape in the orthorhombic and tetragonal phase. The pyroelectric current shows two maxima at 155 and 245 K, corresponding to ferroelectric-ferroelectric and ferroelectric-paraelectric phase transitions, respectively. In particular, the direction of the pyroelectric current can be reversed by a positive or negative poling electric field, which is the assertive evidence of ferroelectricity. The PUND measurements act as the most convincing proof of the ferroelectricity of the MAPbBr3 single crystal. This work reports new evidence of the ferroelectric properties of the MAPbBr3 single crystal, which provides the intrinsic property when considering their high power conversion efficiencies.
