scholarly journals Negative X-Ray Expansion in Cadmium Cyanide

2020 ◽  
Author(s):  
Chloe Coates ◽  
Claire A. Murray ◽  
Hanna Boström ◽  
Emily Reynolds ◽  
Andrew Goodwin
Keyword(s):  
Mechanical Response ◽  
Local Heating ◽  
Negative Thermal Expansion ◽  
Functional Materials ◽  
Temperature Phase ◽  
X Rays ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cadmium Cyanide ◽  
Temperature Phase Transition

Cadmium cyanide, Cd(CN)<sub>2</sub>, is a flexible coordination polymer best studied for its strong and isotropic negative thermal expansion (NTE) effect. Here we show that this NTE is actually X-ray exposure dependent: Cd(CN)<sub>2</sub> contracts not only on heating but also on irradiation by X-rays. This behaviour contrasts that observed in other beam-sensitive materials, for which X-ray exposure drives lattice expansion. We call this effect ‘negative X-ray expansion’ (NXE) and suggest its origin involves an interaction between X-rays and cyanide ‘flips’; in particular, we rule out local heating as a possible mechanism. Irradiation also affects the nature of a low-temperature phase transition. Our analysis resolves discrepancies in NTE coefficients reported previously on the basis of X-ray diffraction measurements, and we establish the ‘true’ NTE behaviour of Cd(CN)<sub>2</sub> across the temperature range 150–750 K. The interplay between irradiation and mechanical response in Cd(CN)<sub>2</sub> highlights the potential for exploiting X-ray exposure in the design of functional materials.

scholarly journals Negative X-Ray Expansion in Cadmium Cyanide

2020 ◽  
Author(s):  
Chloe Coates ◽  
Claire A. Murray ◽  
Hanna Boström ◽  
Emily Reynolds ◽  
Andrew Goodwin
Keyword(s):  
Mechanical Response ◽  
Local Heating ◽  
Negative Thermal Expansion ◽  
Functional Materials ◽  
Temperature Phase ◽  
X Rays ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cadmium Cyanide ◽  
Temperature Phase Transition

Cadmium cyanide, Cd(CN)<sub>2</sub>, is a flexible coordination polymer best studied for its strong and isotropic negative thermal expansion (NTE) effect. Here we show that this NTE is actually X-ray exposure dependent: Cd(CN)<sub>2</sub> contracts not only on heating but also on irradiation by X-rays. This behaviour contrasts that observed in other beam-sensitive materials, for which X-ray exposure drives lattice expansion. We call this effect ‘negative X-ray expansion’ (NXE) and suggest its origin involves an interaction between X-rays and cyanide ‘flips’; in particular, we rule out local heating as a possible mechanism. Irradiation also affects the nature of a low-temperature phase transition. Our analysis resolves discrepancies in NTE coefficients reported previously on the basis of X-ray diffraction measurements, and we establish the ‘true’ NTE behaviour of Cd(CN)<sub>2</sub> across the temperature range 150–750 K. The interplay between irradiation and mechanical response in Cd(CN)<sub>2</sub> highlights the potential for exploiting X-ray exposure in the design of functional materials.

scholarly journals High-temperature phase transition of SrRuO3and SrHfO5: X-ray diffraction and PAC spectroscopy

1996 ◽  
Vol 52 (a1) ◽  
pp. C364-C364
Author(s):  
J. A. Guevara ◽  
S. L. Cuffini ◽  
Y. P. Mascarenhas ◽  
P. de la Presa ◽  
A. Ayala ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Pac Spectroscopy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Temperature Phase Transition

Low Temperature Phase Transition (Pt) and Defect Formation (Df) in Silicon with Dioxide Inclusions Under X-Ray Irradiation

1995 ◽  
Vol 396 ◽  
Author(s):  
SH.M. Makhkamov ◽  
S.N. Abdurakhmanova
Keyword(s):  
Phase Transition ◽  
Charge Exchange ◽  
Defect Formation ◽  
Exchange Process ◽  
Temperature Phase ◽  
X Rays ◽  
Charge Exchange Process ◽  
X Ray ◽  
Temperature Phase Transition ◽  
A Charge

AbstractStudies of galvanomagnetic and electrical parameters of p- type Si : SiO2 in the temperature range 80 – 400 K have shown that X-ray irradiation at 80 K (Mo Ka,β and braking radiation hvmax. = 50 heV) leads to various transformations of the spectrum of electron- hole states in the band gap of such material, depending on the flux density of the X-rays. Two main processes are observed: the defect (vacancy and divacancy) formation and a charge exchange of native defects localized at the Si – SiO2 interface. The charge exchange process is rather collective and stimulated one because it is in response to an X-ray-induced ferroelectric phase transition in the SiO2- phase.

On the Formation of Martensite in In0.77TL0.23.

1990 ◽  
Vol 205 ◽  
Author(s):  
M. Wuttig ◽  
X. Zhou ◽  
S. Nahm ◽  
J. Li
Keyword(s):  
Transformation Temperature ◽  
Mechanical Response ◽  
High Temperature Phase ◽  
Second Phase ◽  
Temperature Phase ◽  
Product Phase ◽  
X Ray Diffraction ◽  
Two Phase ◽  
X Ray ◽  
Precursor Structure

AbstractIt has been proposed that martensite is formed by heterogeneous nucleation and growth or evolves from a precursor. In order to examine these theories, high resolution X-ray diffraction experiments have been performed on In0.77Tl0.23. It is known that the transformation of the alloy is close to second order and tweed has been observed which could be a possible precursor structure. Our experimental results do show precursors but of a different nature: satellites around the 220 Bragg peak have been detected up to 15 degrees above the transformation temperature. They develop reversibly at the angular positions of the product phase. The results are not compatible with the “crest-riding-peridon” model but rather show an equilibrium two phase mixture above the transformation temperature in which the second phase is structurally equal to the product phase. We have also investigated the mechanical response of the high temperature phase and found that both shear ‘elastic constants’ soften. This result can be understood in terms of twin boundary or stacking fault motion.

scholarly journals Synthesis, PtS-Type Structure, and Anomalous Mechanics of the Cd(CN)2 Precursor Cd(NH3)2[Cd(CN)4]

2018 ◽  
Author(s):  
Andrew Goodwin ◽  
Chloe Coates ◽  
Joshua Makepeace ◽  
Andrew Seel ◽  
Mia Baise ◽  
...  
Keyword(s):  
Density Functional ◽  
Mechanical Response ◽  
Variable Temperature ◽  
Negative Thermal Expansion ◽  
Process Variable ◽  
X Ray Diffraction ◽  
Prolonged Heating ◽  
X Ray ◽  
Cadmium Metal ◽  
Nonaqueous Synthesis

We report the nonaqueous synthesis of Cd(CN)<sub>2</sub> by oxidation of cadmium metal with Hg(CN)<sub>2</sub> in liquid ammonia. The reaction proceeds <i>via</i> an intermediate of composition Cd(NH<sub>3</sub>)<sub>2</sub>[Cd(CN)<sub>4</sub>], which converts to Cd(CN)<sub>2</sub> on prolonged heating. Powder X-ray diffraction measurements allow us to determine the crystal structure of the previously-unreported Cd(NH<sub>3</sub>)<sub>2</sub>[Cd(CN)<sub>4</sub>], which we find to adopt a twofold interpenetrating PtS topology. We discuss the effect of partial oxidation on the Cd/Hg composition of this intermediate, as well as its implications for the reconstructive nature of the deammination process. Variable-temperature X-ray diffraction measurements allow us to characterise the anisotropic negative thermal expansion (NTE) behaviour of Cd(NH<sub>3</sub>)<sub>2</sub>[Cd(CN)<sub>4</sub>] together with the effect of Cd/Hg substitution; <i>ab initio</i> density functional theory (DFT) calculations reveal a similarly anomalous mechanical response in the form of both negative linear compressibility (NLC) and negative Poisson's ratios.

Phase Transitions and Distortion of [BiCl6]3– Octahedra in (C3H5NH3)3[BiCl6] – DSC and Single-Crystal X-Ray Diffraction Studies

2004 ◽  
Vol 59 (9) ◽  
pp. 1029-1034 ◽  
Author(s):  
Bartosz Zarychta ◽  
Maciej Bujak ◽  
Jacek Zaleski
Keyword(s):  
Phase Transition ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Unit Cells ◽  
Temperature Phase Transition ◽  
The Relationship ◽  
Low Temperature Phase ◽  
Disorder Type

The DSC diagram of tris(allylammonium) hexachlorobismuthate(III), (C3H5NH3)3[BiCl6], revealed three anomalies at 152, 191 and 299 K. The structure of the salt was determined at 200 and 315 K, below and above the high-temperature phase transition at 299 K. In both phases the crystals are monoclinic. At 200 K the space group is C2/c whereas at 315 K it is C2/m. The structures, at both temperatures, are composed of [BiCl6]3− octahedra and allylammonium cations. The organic and inorganic moieties are attracted to each other by a network of the N-H. . .Cl hydrogen bonds. The relationship between corresponding parameters of the unit cells has been found. The phase transition at 299 K, of the order-disorder type, is attributed to the ordering of one non-equivalent allylammonium cation in the low-temperature phase.

NQR View of Solid Phases of NOCl

1998 ◽  
Vol 53 (6-7) ◽  
pp. 537-541 ◽  
Author(s):  
J. Pirnat ◽  
Z. Trontelj ◽  
H. Borrmann
Keyword(s):  
Phase Transition ◽  
Temperature Phase ◽  
Measured Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Disorder Phase Transition ◽  
Upper Limit ◽  
Temperature Phase Transition ◽  
Solid Phases ◽  
Low Temperature Phase

Abstract Chlorine NQR studies of solid nitrosyl chloride NOC1 between 110 and 212 K are reported. In the temperature dependence an order-disorder phase transition near 145 K, found by X-ray diffraction, is confirmed. Unusual hysteretic NQR signal behaviour indirectly proves also the low temperature phase transition below 100 K. In the measured temperature region fast relaxing mechanisms are present. The upper limit of the expected 14N NQR frequency is estimated using the Townes-Dailey approach.

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