DYNAMICS OF THE LOW TEMPERATURE GLASS-LIKE PHASE IN MANGANITES

2003 ◽  
Vol 17 (04n06) ◽  
pp. 842-847
Author(s):  
C. CASTELLANO ◽  
F. CORDERO ◽  
R. CANTELLI ◽  
M. FERRETTI
Keyword(s):  
Distribution Function ◽  
Phase Transitions ◽  
Quantitative Analysis ◽  
Low Temperature ◽  
Imaginary Part ◽  
Lattice Relaxation ◽  
Relaxation Processes ◽  
Temperature Dependent ◽  
Energy Barriers ◽  
Nanostructured State

We report anelastic spectroscopy measurements of La 1-x Ca x MnO 3 performed in order to better characterize the nature of the phase transitions and microscopic lattice relaxation processes present in these materials. A peak in the imaginary part of the elastic susceptibility presents a behaviour typical of inhomogeneous and glass-like systems. We have performed a quantitative analysis calculating the temperature dependent distribution function of the energy barriers of the fluctuations characterizing this nanostructured state.

Low Temperature Isotope Effect in Ammonium Hexachloroselenate(IV) Studied by 35Cl NQR

1994 ◽  
Vol 49 (1-2) ◽  
pp. 297-301 ◽  
Author(s):  
Y. Kume ◽  
T. Asaji ◽  
R. Ikeda
Keyword(s):  
Relaxation Time ◽  
Phase Transitions ◽  
Low Temperature ◽  
Transition Point ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Soft Modes ◽  
35Cl Nqr

Abstract The temperature dependence o f the 35Cl NQR frequency and spin-lattice relaxation time T1Q of (NH4)2SeCl6 and (ND4)2SeCl6 were measured from 400 K to 24.8 and 53.8 K, respectively. The disappearance of NQR signals in the low temperature region of both salts is attributed to phase transitions. We concluded from the temperature behavior of just above the transition point that the operative mechanism o f the transition is different in these salts: The transition of (ND4)2SeCl6 seems to be associated with rotary soft modes, while in the natural salt non-rotary soft modes seem to play an important role at the transition.

Temperature-Dependent Phase Transitions in Two Crystalline Host–Guest Complexes Derived from Mandelic Acid

1998 ◽  
Vol 54 (1) ◽  
pp. 82-93
Author(s):  
O. Hager ◽  
C. Foces-Foces ◽  
A. L. Llamas-Saiz ◽  
E. Weber
Keyword(s):  
Phase Transitions ◽  
Solid State ◽  
Low Temperature ◽  
Inclusion Complexes ◽  
Mandelic Acid ◽  
Temperature Dependent ◽  
Crystallographic Symmetry ◽  
Crystal Packings

The supramolecular inclusion complexes of two mandelic acid-based chiral host compounds with dimethylformamide (DMF), (1) and (2), show reversible solid–solid state phase transitions upon lowering the temperature. For both inclusion complexes, the low- [(1a) and (2a) at 170 K] and the high- [(1b) at 250 and (2b) at 270 K] temperature structures were solved. (R)-1,1-Bis(4-tert-butylphenyl)-2-phenylethan-1,2-diol–dimethylformamide (1/1), C28H34O2.C3H7NO (1a), T = 170 K, monoclinic, P21, a = 14.4530 (14), b = 6.0540 (2), c = 16.1117 (14) Å, β = 105.332 (7)°, V = 1359.6 (2) Å3, Z = 2, D x = 1.162 g cm−3; (1b), T = 250 K, monoclinic, P21, a = 24.8110 (20), b = 6.0739 (2), c = 18.8645 (10) Å, β = 98.100 (6)°, V = 2814.5 (3) Å3, Z = 4, D x = 1.123 g cm−3. (R)-1,1-Bis(4-tert-butylphenyl)-2-(4-methylphenyl)ethan-1,2-diol–dimethylformamide (1/1), C29H36O2.C3H7NO (2a), T = 170 K, monoclinic, P21, a = 24.4457 (38), b = 5.9519 (6), c = 20.4609 (38) Å, β = 101.95 (1)°, V = 2912.5 (8) Å3, Z = 4, D x = 1.117 g cm−3; (2b), T = 270 K, triclinic, P1, a = 14.4172 (28), b = 6.0303 (4), c = 17.5636 (56) Å, α = 88.74 (1), β = 101.43 (2), γ = 93.13 (1)°, V = 1494.4 (6) Å3, Z = 2, D x = 1.088 g cm−3. The low-temperature forms have the higher crystallographic symmetry. In (1b) half of the DMF guests are twisted by 45.0° with respect to those in (1a). A comparative discussion of the four crystal packings is presented.

On the nature of the phase transitions of aluminosilicate perrhenate sodalite

2020 ◽  
Vol 235 (6-7) ◽  
pp. 213-223
Author(s):  
Hilke Petersen ◽  
Lars Robben ◽  
Thorsten M. Gesing
Keyword(s):  
Raman Spectroscopy ◽  
Phase Transitions ◽  
Decomposition Temperature ◽  
Second Phase ◽  
Structure Property ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
Two Phase ◽  
Structure Property Relationships ◽  
Heat Capacity Measurements

AbstractThe temperature-dependent structure-property relationships of the aluminosilicate perrhenate sodalite |Na8(ReO4)2|[AlSiO4]6 (ReO4-SOD) were analysed via powder X-ray diffraction (PXRD), Raman spectroscopy and heat capacity measurements. ReO4-SOD shows two phase transitions in the investigated temperature range (13 K < T < 1480 K). The first one at 218.6(1) K is correlated to the transition of dynamically ordered $P\overline{4}3n$ (> 218.6(1 K) to a statically disordered (<218.6(1) K) SOD template in $P\overline{4}3n$. The loss of the dynamics of the template anion during cooling causes an increase of disorder, indicated by an unusual intensity decrease of the 011-reflection and an increase of the Re-O2 bond length with decreasing temperature. Additionally, Raman spectroscopy shows a distortion of the ReO4 anion. Upon heating the thermal expansion of the sodalite cage originated in the tilt-mechanism causes the second phase transition at 442(1) K resulting in a symmetry-increase from $P\overline{4}3n$ to $Pm\overline{3}n$, the structure with the sodalites full framework expansion. Noteworthy is the high decomposition temperature of 1320(10) K.

Temperature-induced structural phase transitions in RERhSn (RE = Y, Gd-Tm, Lu)

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Simon Engelbert ◽  
Rolf-Dieter Hoffmann ◽  
Jutta Kösters ◽  
Steffen Klenner ◽  
Rainer Pöttgen
Keyword(s):  
Rare Earth ◽  
Phase Transitions ◽  
Driving Force ◽  
Room Temperature ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
X Ray

Abstract The structures of the equiatomic stannides RERhSn with the smaller rare earth elements Y, Gd-Tm and Lu were reinvestigated on the basis of temperature-dependent single crystal X-ray diffraction data. GdRhSn crystallizes with the aristotype ZrNiAl at 293 and 90 K. For RE = Y, Tb, Ho and Er the HP-CeRuSn type (approximant with space group R3m) is already formed at room temperature, while DyRhSn adopts the HP-CeRuSn type below 280 K. TmRhSn and LuRhSn show incommensurate modulated variants with superspace groups P31m(1/3; 1/3; γ) 000 (No. 157.1.23.1) (γ = 3/8 for TmRhSn and γ = 2/5 for LuRhSn). The driving force for superstructure formation (modulation) is a strengthening of Rh–Sn bonding. The modulation is expressed in a 119Sn Mössbauer spectrum of DyRhSn at 78 K through line broadening.

scholarly journals Tetragonal–Cubic Phase Transition and Low-Field Dielectric Properties of CH3NH3PbI3 Crystals

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4215
Author(s):  
Roxana E. Patru ◽  
Hamidreza Khassaf ◽  
Iuliana Pasuk ◽  
Mihaela Botea ◽  
Lucian Trupina ◽  
...  
Keyword(s):  
Dielectric Properties ◽  
Current Knowledge ◽  
Cubic Phase ◽  
Relaxation Processes ◽  
Temperature Dependent ◽  
Thermally Activated ◽  
Low Field ◽  
Conduction Mechanisms ◽  
Temperature Ranges ◽  
Nyquist Plots

The frequency and temperature dependence of dielectric properties of CH3NH3PbI3 (MAPI) crystals have been studied and analyzed in connection with temperature-dependent structural studies. The obtained results bring arguments for the existence of ferroelectricity and aim to complete the current knowledge on the thermally activated conduction mechanisms, in dark equilibrium and in the presence of a small external a.c. electric field. The study correlates the frequency-dispersive dielectric spectra with the conduction mechanisms and their relaxation processes, as well as with the different transport regimes indicated by the Nyquist plots. The different energy barriers revealed by the impedance spectroscopy highlight the dominant transport mechanisms in different frequency and temperature ranges, being associated with the bulk of the grains, their boundaries, and/or the electrodes’ interfaces.

X-ray study of the low-temperature phase transitions in LiKSO4

1983 ◽  
Vol 4 (1) ◽  
pp. 37-45 ◽  
Author(s):  
P. E. Tomaszewski ◽  
K. Łukaszewicz
Keyword(s):  
Phase Transitions ◽  
Low Temperature ◽  
Temperature Phase ◽  
X Ray ◽  
Low Temperature Phase

In Situ Analysis of Surface Contaminant Desorption during Low-Temperature Silicon Substrate Cleaning using Reflection Electron Energy Loss Spectrometry

1992 ◽  
Vol 259 ◽  
Author(s):  
Selmer S. Wong ◽  
Shouleh Nikzad ◽  
Channing C. Ahn ◽  
Aimee L. Smith ◽  
Harry A. Atwater
Keyword(s):  
Low Temperature ◽  
Energy Loss ◽  
Electron Energy ◽  
Core Loss ◽  
Temperature Dependent ◽  
Electron Energy Loss Spectrometry ◽  
Analysis Technique ◽  
Chemical Analysis Technique ◽  
Electron Energy Loss

ABSTRACTWe have employed reflection electron energy loss spectrometry (REELS), a surface chemical analysis technique, in order to analyze contaminant coverages at the submonolayer level during low-temperature in situ cleaning of hydrogen-terminated Si(100). The chemical composition of the surface was analyzed by measurements of the C K, O K and Si L2,3 core loss intensities at various stages of the cleaning. These results were quantified using SiC(100) and SiO2 as reference standards for C and O coverage. Room temperature REELS core loss intensity analysis after sample insertion reveals carbon at fractional monolayer coverage. We have established the REELS detection limit for carbon coverage to be 5±2% of a monolayer. A study of temperature-dependent hydrocarbon desorption from hydrogen-terminated Si(100) reveals the absence of carbon on the surface at temperatures greater than 200°C. This indicates the feasibility of epitaxial growth following an in situ low-temperature cleaning and also indicates the power of REELS as an in situ technique for assessment of surface cleanliness.

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