Structural phase transitions and their influence on Cu+ mobility in superionic ferroelastic Cu6PS5I single crystals

The structural origin of Cu+ ions conductivity in Cu6PS5I single crystals is described in terms of structural phase transitions studied by X-ray diffraction, polarizing microscope and calorimetric measurements. Below the phase transition at Tc=(144-169) K Cu6PS5I belongs to monoclinic, ferroelastic phase, space group Cc. Above Tc crystal changes the symmetry to cubic superstructure, space group F-43c (a=19.528); finally at 274K disordering of the Cu+ ions increases the symmetry to F-43m, (a=9.794). The phase transition at 274K coincides well with a strong anomaly in electrical conductivity observed in the Arrhenius plot. Diffusion paths for Cu+ ions are evidenced by means of the atomic displacement factors and split model. Influence of the copper stechiometry on the Tc is also discussed.Comment: conference pape

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

Ceria nanoparticles deposited on graphene nanosheets for adsorption of copper(II) and lead(II) ions and of anionic species of arsenic and selenium

A nanocomposite prepared from graphene nanosheets and cerium nanoparticles (G/CeO) was applied to the extraction of Se(IV), As(V), As(III), Cu(II) and Pb(II). The structure of G/CeO was investigated by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The optimal pH values for extraction are 4.0 for As(V), 3.0 for Se(IV), and 6.0 for both Cu(II) and Pb(II). The maximum adsorption capacity of G/CeO (expressed as mg·g) were calculated by the Langmuir model and are found to be 8.4 for As(V), 14.1 for Se(IV), 50.0 for Cu(II) and 75.6 for Pb(II). The sorbent was applied to dispersive solid phase microextraction prior to direct quantitation by energy-dispersive X-ray fluorescence spectrometry without the need for prior elution. The limits of detection (in ng·mL units) are 0.10 for As(V), 0.11 for Se(IV), 0.19 for Cu(II) and 0.21 for Pb(II). The precisions (RSDs) are <4.5%. The accuracy of the method (1 - 4%) was verified by analysis of the certified reference material (CRM 1640a - natural water). The method was successfully applied in ultratrace element determination and to the speciation of selenium in environmental waters

The phase transitions in CsFe MoO4 2 triangular lattice antiferromagnet, neutron diffraction and high pressure studies

We report on the phase transitions in the triangular lattice antiferromagnet CsFe MoO4 2 at low temperatures and high pressure using powder neutron and X ray diffraction, specific heat, magnetic susceptibility and in situ high pressure Raman measurements. CsFe MoO4 2 undergoes a structural phase transition induced by the rotation of MoO4 2 tetrahedra at Tc 220 K. The transformation is associated with a symmetry decrease from P 3m to P 3. Below 4.5 K the antiferromagnetic long range order appears that is related to the nuclear unit cell by the modulation vector q 1 3 1 3 0.5 . The system adopts 120 spiral spin structure that has been found in several triangular lattice multiferroics. Under pressure CsFe MoO4 2 undergoes a reconstructive phase transition to a much larger superstructure which preserves the super exchange interactions at low temperatures and allows an additional magnetic long range order at T 20

Piezoelectricity and crystal structure of H-beta-(2-Pyridy1)-Ala-OH amino acid microcrystals

Self-assembled peptide nanotubes (PNT) are unique nanoscale objects having a great potential for a multitude of applications. We report the congeneric studies on local piezoelectric properties of H-beta-(2-Pyridy1)-Ala-OH. It crystallizes in needle shaped microcrystals of the size from the fraction of micrometer up to tens of micrometers. The structure of this amino acid was determined by means of X-ray single crystal diffraction. At room temperature the amino acid crystals exhibit strong piezoelectric properties which were studied using piezoelectric force microscopy (PFM). Moreover the optical and scanning electron microscope (SEM) observations were carried out, the thermal stability was determined (TGA method). (C) 2014 Elsevier B.V. All rights reserved

Phase sequence in diisopropylammonium iodide: avoided ferroelectricity by the appearance of a reconstructed phase

Crystals of diisopropylammonium iodide are synthesized, grown and characterized. Two phases: P21/m (Z = 1) and P212121 (Z = 2) are observed. In contrast with analogous compounds no polar phase occurs, despite a critical-like electric behaviour. A phenomenological theory is proposed to describe the thermodynamics of the whole family of diisopropylammonium halides