Ryszard Jakubas

Bio: Ryszard Jakubas is an academic researcher from University of Wrocław. The author has contributed to research in topics: Phase transition & Dielectric. The author has an hindex of 36, co-authored 330 publications receiving 5423 citations.

Phase transitions in alkylammonium halogenoantimonates and bismuthates

Abstract: A review of the results of studies on the structure, phase transitions and physical properties of alkylammonium halogenoantimonates (III) and bismuthates (III) is presented. The crystals of these compounds are characterized by a variety of anionic structures and show a number of phase transitions including those to polar phases. We concentrate here mainly on dielectric and pyroelectric properties, spontaneous polarization and DSC studies. The mechanism of the phase transitions is discussed based on the results of X-ray, dielectric relaxation, PMR, IR and R spectra studies gathered so far. A particular role is played by a reorientational motion of the alkylammonium cations.

Flexible ferroelectric organic crystals.

Abstract: Flexible organic materials possessing useful electrical properties, such as ferroelectricity, are of crucial importance in the engineering of electronic devices. Up until now, however, only ferroelectric polymers have intrinsically met this flexibility requirement, leaving small-molecule organic ferroelectrics with room for improvement. Since both flexibility and ferroelectricity are rare properties on their own, combining them in one crystalline organic material is challenging. Herein, we report that trisubstituted haloimidazoles not only display ferroelectricity and piezoelectricity-the properties that originate from their non-centrosymmetric crystal lattice-but also lend their crystalline mechanical properties to fine-tuning in a controllable manner by disrupting the weak halogen bonds between the molecules. This element of control makes it possible to deliver another unique and highly desirable property, namely crystal flexibility. Moreover, the electrical properties are maintained in the flexible crystals.

Structure and phase transition in (CH3NH3)3Bi2Br9. A novel improper ferroelectrics

Abstract: The crystals of (CH3NH3)3Bi2Br9 have been grown which at room temperature are isomorphous with Cs3Bi2Br9 and (CH3NH3)3Sb2Br9. The space group is P3m1, a = 0.807, c = 1.008 nm, V = 0.5685 nm3, Z = 1. The crystals reveal, when cooling, three phase transitions at 188 ± 0.5, 140 ± 1, and 101.5 ± 0.5 K. The high temperature phase (I) behaves as a plastic one with respect to a freedom of rotation of methylammonium cations. The two high temperature transitions I II and II III can be related, similarly to (CH3NH3)3Sb2Br9, to a freezing of reorientation of those cations. At 101.5 K a transition to the improper ferroelectric phase IV was discovered. The features of this phase are non-typical and the nature of the transition is unknown.

Structure and ferroelectric properties of ( C 3 N 2 H 5 ) 5 Bi 2 Cl 11

Abstract: Pentakis (imidazolium) undecachlorodibismuthate(III), ${({\mathrm{C}}_{3}{\mathrm{N}}_{2}{\mathrm{H}}_{5})}_{5}{\mathrm{Bi}}_{2}{\mathrm{Cl}}_{11}$, has been synthesized and studied by means of the x-ray, differential scanning calorimetry (DSC), and dielectric methods over a wide temperature range. The room temperature crystal structure has been determined as monoclinic, space group $P{2}_{1}∕n$ with $a=13.616\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, $b=14.684\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, $c=9.045\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, and $\ensuremath{\beta}=96.85\ifmmode^\circ\else\textdegree\fi{}$. Two solid--solid phase transitions: $P\overline{4}n2\stackrel{360\phantom{\rule{0.3em}{0ex}}\mathrm{K}}{\ensuremath{\rightarrow}}P{2}_{1}∕n$ $(I\ensuremath{\rightarrow}II)$, and $P{2}_{1}∕n\stackrel{166\phantom{\rule{0.3em}{0ex}}\mathrm{K}}{\ensuremath{\rightarrow}}P{2}_{1}$ $(II\ensuremath{\rightarrow}III)$, discontinuous and continuous in nature, respectively, have been revealed. The dielectric and pyroelectric measurements allow us to characterize the lowest temperature phase (III) as ferroelectric with the Curie point at $166\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and saturated spontaneous polarization value of the order of $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.3em}{0ex}}\mathrm{C}\phantom{\rule{0.2em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}$ along the $\mathbit{b}$ axis. The ferroelectric phase transition mechanism is governed by the dynamics of imidazolium cations. The room temperature, paraelectric phase (II) demonstrates additionally the ferroelastic properties.

Halide Perovskite Photovoltaics: Background, Status, and Future Prospects

Abstract: The photovoltaics of organic–inorganic lead halide perovskite materials have shown rapid improvements in solar cell performance, surpassing the top efficiency of semiconductor compounds such as CdTe and CIGS (copper indium gallium selenide) used in solar cells in just about a decade. Perovskite preparation via simple and inexpensive solution processes demonstrates the immense potential of this thin-film solar cell technology to become a low-cost alternative to the presently commercially available photovoltaic technologies. Significant developments in almost all aspects of perovskite solar cells and discoveries of some fascinating properties of such hybrid perovskites have been made recently. This Review describes the fundamentals, recent research progress, present status, and our views on future prospects of perovskite-based photovoltaics, with discussions focused on strategies to improve both intrinsic and extrinsic (environmental) stabilities of high-efficiency devices. Strategies and challenges regardi...

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Bismuth Based Hybrid Perovskites A3Bi2 I9 (A: Methylammonium or Cesium) for Solar Cell Application.

Abstract: Low-toxic bismuth-based perovskites are prepared for the possible replacement of lead perovskite in solar cells. The perovskites have a hexagonal crystalline phase and light absorption in the visible region. A power conversion efficiency of over 1% is obtained for a solar cell with Cs3 Bi2 I9 perovskite, and it is concluded that bismuth perovskites have very promising properties for further development in solar cells.

Identifying defect-tolerant semiconductors with high minority-carrier lifetimes: beyond hybrid lead halide perovskites

Abstract: The emergence of methyl-ammonium lead halide (MAPbX3) perovskites motivates the identification of unique properties giving rise to exceptional bulk transport properties, and identifying future materials with similar properties. Here, we propose that this “defect tolerance” emerges from fundamental electronic-structure properties, including the orbital character of the conduction and valence band extrema, the chargecarrier effective masses, and the static dielectric constant. We use MaterialsProject.org searches and detailed electronic-structure calculations to demonstrate these properties in other materials than MAPbX3. This framework of materials discovery may be applied more broadly, to accelerate discovery of new semiconductors based on emerging understanding of recent successes.