RESUMEN
By controlling the supersaturation and choosing high-quality seeds, we successfully suppress the prismatic growth of the tetragonal potassium dihydrogen phosphate (KDP) SCFs, realize the rapid growth along the [001] direction, and obtain SCFs less than 10 µm in width with lengths of centimeters. The experimental results show that there exist critical supersaturation points, 22.40% and 41.41% at 25 °C, for initiating the growth of KDP SCF on its pyramidal and prismatic faces, respectively, which are quite different from those of the bulk crystals. We use the mechanism of 2D nucleation on smooth faces to explain the peculiar phenomena, assuming that there is no 2D or 3D defect on the surfaces of the seed fiber crystal. The assumption is supported by AFM observation of the surface micromorphology of the SCFs. Our solution growth technique developed can be used to grow ultrafine SCFs unable to be achieved by existing melt growth techniques.
RESUMEN
To study stability issues of three-dimensional perovskites, there is a strategy to introduce the thiocyanate ion (SCN-) into CH3NH3PbI3 (MAPbI3) to solve these problems. Here, we report the bulk growth of layered perovskite MA2Pb(SCN)2I2 single crystals by different growth methods in an ambient atmosphere. We also investigate the structural determination and refinements, band gap, and photoluminescence of MA2Pb(SCN)2I2 single crystals. More importantly, the phase transition and stability of MA2Pb(SCN)2I2 are systematically demonstrated. MA2Pb(SCN)2I2 undergo the reversible single-crystal to single-crystal phase transition in the orthorhombic systems from the space group Pmmn (no. 59) to the space group Pmn21 (no. 31) at low temperature. Moreover, the temperature-dependent recovery behaviors of MA2Pb(SCN)2I2 single crystals, powders, and thin films at high temperature are studied in detail. Besides, the moisture stability of MA2Pb(SCN)2I2 is described when exposed to moisture condition by the experiment and theoretical calculations. It would be interesting to not only conduct a comprehensive study on the crystal structures and the phase transition processes of layered perovskites but also provide guidance for further optoelectronic applications of these perovskite materials.
RESUMEN
Motivated by the chirality research of the hybrid halide perovskite, we reported the controllable growth of single crystals of (R)-, (S)-, and (R,S)-C6H5CH(CH3)NH3 (MBA)-based lead (Pb) halide perovskites. The crystal structures were redetermined and further refined to clarify the previously ambiguous crystal structure problems. We further investigated the chiral optical properties of these single crystals including nonlinear optical (NLO) properties and photoluminescence (PL) properties. The as-fabricated (R)- and (S)-MBAPbBr3 single crystals not only show notable circular dichroism (CD) signals in the absorption spectra but also exhibit obvious circularly polarized luminescence (CPL) characteristics. The available chiral hybrid perovskite single crystals open up the possibility to study these intrinsic chirality properties for optoelectronic applications.