Search

A defining property of ferroelectricity is the switching between different states by the application of an electric field. Hysteresis loops serve like a fingerprint of ferroelectric materials giving some useful information. Sometimes the interpretation of information extracted from hysteresis measurements can be challenging due to the non-ferroelectric factors such as electrical conductivity, defect dipole presence and/or dielectric properties. In this paper, the ferroelectric and non-ferroelectric factors on P–E hysteresis loops were investigated in a CuInP2S6-type single crystal. The analysis of data obtained for this single crystal allowed extracting the reliable values in the materials with a low polarization and a high conductivity.

In this paper we report a dielectric study on four single crystals Pb2P2S6, (Pb0.98Ge0.02)2P2S6, (Pb0.7Sn0.3)2P2S6 + 5% Ge and (Pb0.7Sn0.3)2P2Se6 + 5% Ge down to 20 K. A new quantum paraelectric state was reported in the Ge-doped samples at low temperatures. In all of these materials the non-classical T2 temperature dependences of inverse dielectric permittivity were observed. The dielectric constants of Pb2P2S6-based single crystals were measured between 20 and 300 K. The temperature dependences of dielectric permittivity were analysed on the basis of Barrett’s model as a signature of quantum paraelectricity.

NewSQL maturity level analysis

Manoeuvring in limited spaces of car parks causes a lot of problems for drivers trying to park as well as drivers entering or leaving parking lots. The main problems include traffic jams, unexpected car accidents, and concentration of exhaust gases. Analysis of parking manoeuvres and creation of traffic management algorithms for closed spaces lead to effective planning of management of such processes and allow securing safety regardless of human element. This article presents a modernised stand model of a multi-storey car park, algorithms for modelled situations and their management programs.

The room temperature ionic liquid (RTIL) 1-decyl-3-methyl-imidazolium bromide [C10mim][Br], dissolved in water, was studied using 1H and 13C NMR spectroscopy. The manifestation of phase transitions and fine features of molecular motion in NMR spectra upon changing temperature and composition have been analyzed. The 1H NMR line shape typical for anisotropic fluids with zero biaxiality (asymmetry) of magnetic shielding and the chemical shift anisotropy (CSA) of ca 0.33 ppm was observed and attributed to water molecules. CSA values for 13C nuclei have been found in the range of 1.2–1.7 ppm. The difference between lyotropic liquid-crystalline (LC) ionogel phase and the solid one has been revealed, where the motions of RTIL and water molecules have been found to be dynamically segregated. The anisotropic 13C NMR signal shape at 16.89 ppm shows the difference between LC ionogel and the lamellar phases, where usually the decreasing order parameter moving along hydrocarbon chain from the polar head is observed. It indicates that the terminal –CH3 groups are more ordered and the supramolecular structures of [C10mim][Br], similar to some higher micellar RTIL aggregates are expected. In order to explain the experimental observations, the quantum chemistry DFT calculations of 1H and 13C magnetic shielding tensors of [C10mim][Br] and various H-bond structures of H2O were performed. Keywords: properties of molecules and molecular ions, line and bands widths, shapes and shifts, NMR and relaxation

The ionic liquid 1-decyl-3-methyl-imidazolium bromide [C10mim][Br], the neat material, and also dissolved (~0.01 mole fraction) in various dielectric media (acetonitrile, benzene, chloroform, dichloromethane, methanol, 2-butanol and H2O) was studied using 1H and 13C NMR spectroscopy. The most important interaction in this compound is considered to be the Br-...H-C2+ hydrogen bond, which is formed between the anions and cations. The obtained results show that dielectric medium influence mostly the behavior of the Br-...H-C2+ bridge proton. The changes observed in 1H and 13C NMR spectra of [C10mim][Br] with increasing solvents polarity and temperature can be explained applying the model of the lengthening of the H2...Br- bond with the accompanying thickening of the solvation shell of bromine anion and C2-H bond contraction. The short-range order effects related to the configuration of neighboring dipoles of solvent molecules are more important for the solvation ability of small anions than the bulk solvent field effect. However, the solvents, molecules of which tend to associate via hydrogen bonding, can significantly affect the dynamics of anions.

Šiai dienai ypač populiarūs ferroelektrikai susidedantys iš kelių feroiškai aktyvių subgardelių, kurių persitvarkymas fazinio virsmo temperatūroje atskleidžia naujų, dar neaprašytų reiškinių. Prie šių medžiagų priskiriami antiferoelektrikai, ferielektrikai ir multiferoikai. Šiame darbe buvo tiriama nauja medžiagų šeimos MNP2X6 (M = Cu, Ag; N=In, Cr, Bi; X=S, Se ), kurios pasižymi ferielektrinėmis bei multiferoinėmis savybėmis, ir kurių dielektrines ir elektrines savybes galima efektyviai keisti įvedant priemaišas. Minėtų medžiagų dielektrinės ir elektrinės savybės buvo tiriamos dielektrinės spektroskopijos metodais, kurie leidžia tirti kristalų kolektyvinius reiškinius susijusius su tvarkos – netvarkos bei poslinkio tipo faziniais virsmais, jonų migracija bei dipolių užšalimu (stiklėjimu) plačiame dažnių (10-5 Hz iki 3 GHz) bei temperatūrų (25 K iki 500 K) intervaluose. Įvedus 10% Ag jonų vietoj Cu jonų ferielektriniame kristale CuInP2S6 fazinio virsmo temperatūra pasislenka į žemesnias temperatūras, o padidinus indžio koncentraciją fazinio virsmo temperatūra pasislenka į aukštesnes temperatūras. Minėtų kristalų fazinių virsmų temperatūrų skirtumas 50 K. Sumaišius skirtingomis proporcijomis feroelektriką (CuInP2S6) su antiferoelektriku (CuCrP2S6) stebima dipolinio stiklo fazė. Iš dielektrinių matavimų stiklo fazėje buvo paskaičiuota relaksacijos trukmių pasiskirstymo funkcija, kurios aprašymas dvigubos potencialinės duobės modeliu leido susieti mikroskopinius kristalo... [toliau žr. visą tekstą] Nowadays the ferroelectrics containing of several feroically active sublattices are very attractive, because interactions between these sublattices can caused novel phenomena. Antiferroelectrics, ferrielectrics and multiferoics belong to these materials. In this work new crystalline materials MNP2X6 (M = Cu, Ag; N=In, Cr, Bi; X=S, Se) were investigated, which have ferrielectric and multiferoic properties. The dielectric and electric properties of above mentioned materials have been investigated by broadband dielectric spectroscopy methods, which allows to analyze the collective processes related to order – disorder and displacive phase transitions, ions migration and freezing of dipoles (glassy state) in wide temperature (25 K - 500 K) and frequency (10-5 HZ - 3 GHz) ranges. By substitution or doping it becomes possible to tailor the ferroelectric materials to different properties. In this work is determined that the substitution of 10% Cu ions by Ag ions shifts the phase transition temperature of CuInP2S6 crystal toward lower temperatures while the addition of In ions shifts the phase transitions temperature toward the higher ones. The phase transition temperature difference is about 50 K for mentioned crystals. If the ferroelectric crystal CuInP2S6 is mixed with the antiferroelectric CuCrP2S6 the dipole glass phase occupies the middle of the phase diagram. The distribution of relaxation times has been calculated from the broadband dielectric spectra of dipolar glasses. The... [to full text]

Nowadays the ferroelectrics containing of several feroically active sublattices are very attractive, because interactions between these sublattices can caused novel phenomena. Antiferroelectrics, ferrielectrics and multiferoics belong to these materials. In this work new crystalline materials MNP2X6 (M = Cu, Ag; N=In, Cr, Bi; X=S, Se) were investigated, which have ferrielectric and multiferoic properties. The dielectric and electric properties of above mentioned materials have been investigated by broadband dielectric spectroscopy methods, which allows to analyze the collective processes related to order – disorder and displacive phase transitions, ions migration and freezing of dipoles (glassy state) in wide temperature (25 K - 500 K) and frequency (10-5 HZ - 3 GHz) ranges. By substitution or doping it becomes possible to tailor the ferroelectric materials to different properties. In this work is determined that the substitution of 10% Cu ions by Ag ions shifts the phase transition temperature of CuInP2S6 crystal toward lower temperatures while the addition of In ions shifts the phase transitions temperature toward the higher ones. The phase transition temperature difference is about 50 K for mentioned crystals. If the ferroelectric crystal CuInP2S6 is mixed with the antiferroelectric CuCrP2S6 the dipole glass phase occupies the middle of the phase diagram. The distribution of relaxation times has been calculated from the broadband dielectric spectra of dipolar glasses. The double potential well model for the distribution of relaxation times reveals the relation between the macroscopic and microscopic parameters of the dipolar glasses. Also the contribution of domain walls dynamics was separated from the dipole glass freezing in PGO and CuBiP2Se6 crystals.

The dielectric properties of newly synthesized Ag0.1Cu0.9InP2S6 crystals were investigated in broad frequency (20 Hz – 1 MHz) and temperature range (110 K – 350 K). Anomaly in the temperature dependence of a complex dielectric permittivity indicating the polar phase transition was detected at the temperature 283 K . The dielectric properties of the presented crystal are mainly caused by conductivity and phase transition. The frequency spectra of the conductivity obey the Almond-West power law. The activation energy of the conductivity was found to be EA/k= 6381 K. A suggestion is given that the electric conductivity in these crystals can be interpreted by ionic mechanism. The piezoelectric sensitivity was observed only when DC bias electric field was applied along direction normal to layers. In this case the piezoelectric sensitivity appeared due to electrostriction.

The dielectric properties of newly synthesized Ag0.1Cu0.9InP2S6 crystals were investigated in broad frequency (20 Hz – 1 MHz) and temperature range (110 K – 350 K). Anomaly in the temperature dependence of a complex dielectric permittivity indicating the polar phase transition was detected at the temperature 283 K. The dielectric properties of the presented crystal are mainly caused by conductivity and phase transition. The frequency spectra of the conductivity obey the Almond-West power law. The activation energy of the conductivity was found to be EA/k= 6381 K. A suggestion is given that the electric conductivity in these crystals can be interpreted by ionic mechanism. The piezoelectric sensitivity was observed only when DC bias electric field was applied along direction normal to layers. In this case the piezoelectric sensitivity appeared due to electrostriction. Ištirtos dielektrinės ir ultragarsinės Ag0,1Cu0,9InP2S6 kristalo savybės. Dielektrinės skvarbos spektrai buvo matuojami žemųjų (20-106 Hz) srityse. Matuota kristalą šaldant nuo 350 K iki 110 K temperatūros. Kompleksinės dielektrinės skvarbos ε* realiosios ir menamosios dalių priklausomybės nuo temperatūros parodo, kad kristale reiškiasi dielektrinė dispersija – dielektrinės skvarbos priklausomybė nuo elektrinio lauko kitimo dažnio. Tiek iš realiosios, tiek iš menamosios dielektrinės skvarbos temperatūrinių priklausomybių galima išskirti dvi būdingąsias sritis: joninio laidumo ir fazinio virsmo sąlygotas dielektrinės skvarbos dispersijas. Žemojo dažnio srityje ir aukštoje temperatūroje (T > 290 K) dispersiją sąlygoja tūrinis kristalo laidumas. Dėl fazinio virsmo atsirandanti dispersija matyti visoje matuotų dažnių srityje ir temperatūroje, artimoje fazinio virsmo temperatūrai (T ≈ 283 K).

Ferroelectric phosphorous chalcogenide family investigated in this doctoral dissertation can be subdivided into two compounds groups. The first group is represented by the general formula M2P2X6 (where M - transition metal, X – chalcogenides), and can be classified as ternary phosphorus chalcogenides. The second crystal group is described by Van der Waals layered structure with the common chemical formula MIMIIIP2X6 (where MI, MIII – transition metals, X – chalcogenides). Most of these compounds are characterized by compact arrangement of chalcogen atoms, in which two atom layers of phosphorus and a layer of metal atoms placed between them construct the two-dimensional fragments in form of a sandwich. The main aim of this doctoral dissertation is to investigate the dielectric, ferroelectric, pyroelectric and noise properties related to the phase transitions of ternary and quaternary phosphorus chalcogenide crystals. The ferroelectric properties of the nominally pure ternary phosphorus chalcogenide Sn2P2S6 crystal has been investigated in this dissertation. The influence of various impurities on the dielectric, electrical and ferroelectric properties of the mixed crystals is also investigated. The copper indium thiophosphate (CuInP2S6) is the most prominent example of the quaternary phosphorus chalcogenides. Up till now, the structural and physical properties of CuInP2S6 bulk and nanoscale crystals have been extensively studied and reviewed. In this dissertation the low-frequency noise characteristics of the well-studied lamellar ferrielectric-semiconductor CuInP2S6 crystal were explored.