Suppression of phase transitions and glass phase signatures in mixed cation halide perovskites

Cation engineering provides a route to control the structure and properties of hybrid halide perovskites, which has resulted in the highest performance solar cells based on mixtures of Cs, methylammonium, and formamidinium. Here, we present a multi-technique experimental and theoretical study of structural phase transitions, structural phases and dipolar dynamics in the mixed methylammonium/dimethylammonium MA1-xDMAxPbBr3 hybrid perovskites (0 ≤ x ≤ 1). Our results demonstrate a significant suppression of the structural phase transitions, enhanced disorder and stabilization of the cubic phase even for a small amount of dimethylammonium cations. As the dimethylammonium concentration approaches the solubility limit in MAPbBr3, we observe the disappearance of the structural phase transitions and indications of a glassy dipolar phase. We also reveal a significant tunability of the dielectric permittivity upon mixing of the molecular cations that arises from frustrated electric dipoles

Introduction effort, climate matching and species traits as predictors of global establishment success in non-native reptiles

Non-native reptiles are often detrimental to native communities and ecosystems and can be extremely difficult to manage once established. Thus, there is considerable interest in predicting the likelihood of establishment of nonnative reptiles. We assessed three hypotheses describing possible factors contributing to the successful establishment of introduced reptiles in an effort to better identify potential invaders

Suppression of phase transitions and glass phase signatures in mixed cation halide perovskites

Cation engineering provides a route to control the structure and properties of hybrid halide perovskites, which has resulted in the highest performance solar cells based on mixtures of Cs, methylammonium, and formamidinium. Here, we present a multi-technique experimental and theoretical study of structural phase transitions, structural phases and dipolar dynamics in the mixed methylammonium/dimethylammonium MA1-xDMAxPbBr3 hybrid perovskites (0 ≤ x ≤ 1). Our results demonstrate a significant suppression of the structural phase transitions, enhanced disorder and stabilization of the cubic phase even for a small amount of dimethylammonium cations. As the dimethylammonium concentration approaches the solubility limit in MAPbBr3, we observe the disappearance of the structural phase transitions and indications of a glassy dipolar phase. We also reveal a significant tunability of the dielectric permittivity upon mixing of the molecular cations that arises from frustrated electric dipoles

Dielectric spectroscopy of BaTiO3_{3} confined in MCM-41 mesoporous molecular sieve materials

Dielectric properties of Barium titanate particles, synthesized directly in the pores of MCM-41 materials, have been investigated in the frequency range from 20 Hz to 1 MHz for temperature interval from 100 K to 500 K. The pore diameters were 2.0 nm, 2.5 nm and 3.7 nm, and thus the synthesized particles size was already below the critical size of BaTiO$_{3}$. The dielectric spectra of Barium titanate confined in these molecular sieves were compared with the results obtained from the investigation of pure MCM-41 materials. Obtained results confirmed successful incorporation of BaTiO$_{3}$ into porous matrix but no phase transition from paraelectric to ferroelectric phase was observed due to the particle size being smaller than the critical size. Also the overall dielectric response of investigated materials is strongly influenced by adsorbed water molecules

Dielectric Spectroscopy of Water Dynamics in Functionalized UiO-66 Metal-Organic Frameworks

We present a dielectric spectroscopy study of dipolar dynamics in the hydrated UiO-66(Zr) type metal-organic frameworks (MOFs) functionalized with −NH2 and −F groups. Experiments are performed in a broad temperature and frequency ranges allowing us to probe several dipolar relaxations. For both samples at temperature below 220 K, we observe confined supercooled water dynamics, which can be described by the Arrhenius law. At slightly higher temperature, a second less pronounced dipolar relaxation is identified, and its origin is discussed. At even higher temperature, the dielectric permittivity exhibits anomalous increase with increasing temperature due to the proton conductivity. Upon further heating, the permittivity shows a sudden decrease indicating a reversible removal of water molecules. Measurements of the dehydrated samples reveal absence of all three dipolar processes

Growth and Investigation of Heterostructures Based on Multiferroic BiFeO3BiFeO_3

We report heteroepitaxial growth of multiferroic $BiFeO_3$ thin films by RF magnetron sputtering on lattice-matched $SrTiO_3$ substrates, as well as preparation and electrical properties of the heterostructures formed by growing $BiFeO_3$ thin films on highly conductive $LaNiO_3$ films and n-Si substrates. Nonlinear and rectifying current-voltage (I-U) characteristics were revealed for the heterojunctions in a wide temperature range (T=78-300 K)