Specific Heat of MnCoGe Type Compounds at Martensitic Phase Transitions

2012 ◽  
Vol 190 ◽  
pp. 331-334 ◽  
Author(s):  
P.E. Markin ◽  
N.V. Mushnikov ◽  
A.V. Proshkin ◽  
S.V. Belyaev
Keyword(s):  
Phase Transitions ◽  
Specific Heat ◽  
Structural Transition ◽  
Elevated Temperatures ◽  
Type Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
Martensitic Phase Transitions ◽  
Type Transition

The X-ray diffraction and specific heat measurements have been performed for the ferromagnetic compounds (MnCo)1-xGe within the concentration range 0.02 x 0.035. The compounds possess the hexagonal Ni2In-type structure at elevated temperatures, while for the composition with x = 0.02 and 0.03 a spontaneous martensitic-type transition to the orthorhombic TiNiSi-type phase occurs at 283 and 221 K, respectively. We studied the entropy changes associated with the first-order structural transition and estimated the changes in magnetic, lattice, electronic entropies.

scholarly journals Thermal evolution of the crystal structure and phase transitions of KNbO 3

2018 ◽  
Vol 5 (6) ◽  
pp. 180368 ◽  
Author(s):  
S. L. Skjærvø ◽  
K. Høydalsvik ◽  
A. B. Blichfeld ◽  
M.-A. Einarsrud ◽  
T. Grande
Keyword(s):  
Crystal Structure ◽  
Phase Transitions ◽  
Thermal Evolution ◽  
Dynamical Instability ◽  
X Ray Diffraction ◽  
Two Phase ◽  
X Ray ◽  
Cell Parameters ◽  
First Order ◽  
Heating And Cooling

The thermal evolution of the crystal structure and phase transitions of KNbO 3 were investigated by high-temperature powder X-ray diffraction and Rietveld refinement of the diffraction data. Two phase transitions from orthorhombic ( Amm 2) to tetragonal ( P 4 mm ) and from tetragonal to cubic ( P m 3 ¯ m ) were confirmed, both on heating and cooling. Both phase transitions are first order based on the observed hysteresis. The mixed displacive and order–disorder nature of the tetragonal to cubic transition is argued based on symmetry and apparent divergence of the atomic positions from pseudo-cubic values. The transition between the orthorhombic and tetragonal phase shows no temperature-dependence for atomic positions and only thermal expansion of the unit cell parameters and is thus discussed in relation to a lattice dynamical instability.

OBSERVATION OF PHASE TRANSITIONS AT THE (100) SURFACE OF Al-3 at.% Ag

1995 ◽  
Vol 02 (02) ◽  
pp. 141-145 ◽  
Author(s):  
E. WETLI ◽  
M. HOCHSTRASSER ◽  
D. PESCIA ◽  
M. ERBUDAK
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Photoelectron Spectroscopy ◽  
Short Range ◽  
Short Range Order ◽  
Elevated Temperatures ◽  
X Ray ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase

In the bulk binary alloy Al-3 at.% Ag , Ag 2 Al precipitates are formed below 410°C which are reversibly dissolved at elevated temperatures. We have followed this phase transition at a (100) surface as a function of temperature by monitoring the bandwidth of the Ag 4d states in X-ray photoelectron spectroscopy. Since the bandwidth measures the coordination number of the emitting atoms, it directly reveals the short-range order of the Ag atoms at the surface. The measurements show that the dissolution of the Ag -rich clusters starts at temperatures at least 100 K below the bulk transition, and the observed hysteresis behavior is indicative of a first-order phase transition at the surface.

scholarly journals Studies of Optical, Dielectric, Ferroelectric, and Structural Phase Transitions in 0.9[KNbO3]-0.1 [BaNi1/2Nb1/2O3−δ]

Crystals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 35
Author(s):  
Blanca Yamile Rosas ◽  
Alvaro A. Instan ◽  
Karuna Kara Mishra ◽  
S. Nagabhusan Achary ◽  
Ram S. Katiyar
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Structural Phase ◽  
Cubic Phase ◽  
Structural Phase Transitions ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
X Ray ◽  
Wide Range

The compound 0.9[KNbO3]-0.1[(BaNi1/2Nb1/2O3−δ] (KBNNO), a robust eco-friendly (lead-free) ferroelectric perovskite, has diverse applications in electronic and photonic devices. In this work, we report the dielectric, ferroelectric, and structural phase transitions behavior in the KBNNO compound using dielectric, X-ray diffraction, and Raman studies at ambient and as a function of temperature. Analyses of X-ray diffraction (XRD) data at room temperature (rtp) revealed the orthorhombic phase (sp. Gr. Amm2) of the compound with a minor secondary NiO cubic phase (sp. Gr. Fm3m). A direct optical band gap Eg of 1.66 eV was estimated at rtp from the UV–Vis reflectance spectrum analysis. Observation of non-saturated electric polarization loops were attributed to leakage current effects pertaining to oxygen vacancies in the compound. Magnetization studies showed ferromagnetism at room temperature (300 K) in this material. XRD studies on KBNNO at elevated temperatures revealed orthorhombic-to-tetragonal and tetragonal-to-cubic phase transitions at 523 and 713 K, respectively. Temperature-dependent dielectric response, being leaky, did not reveal any phase transition. Electrical conductivity data as a function of temperature obeyed Jonscher power law and satisfied the correlated barrier-hopping model, indicating dominance of the hopping conduction mechanism. Temperature-dependent Raman spectroscopic studies over a wide range of temperature (82–673 K) inferred the rhombohedral-to-orthorhombic and orthorhombic-to-tetragonal phase transitions at ~260, and 533 K, respectively. Several Raman bands were found to disappear, while a few Raman modes such as at 225, 270, 289, and 831 cm−1 exhibited discontinuity across the phase transitions at ~260 and 533 K.

Kubische Cyanomercurate NR4MHg(CN)4 (R = Et, Pr; M = Li, Na, K, Cu) mit Alumosilikatstruktur/On Cubic Cyanomercurates NR4MHg(CN)4 (R = Et, Pr; M = Li, Na, K, Cu) with Alumosilicate Type Structure

1986 ◽  
Vol 41 (11) ◽  
pp. 1346-1350 ◽  
Author(s):  
Gerhard Thiele ◽  
Joachim Großmann ◽  
Albert Wolfgang Pürzer
Keyword(s):  
Three Dimensional ◽  
Type Structure ◽  
X Ray Diffraction ◽  
Polar Solvents ◽  
Space Group ◽  
X Ray ◽  
First Order ◽  
Structure Determinations ◽  
Cubic Forms ◽  
Reversible Phase

Abstract Quaternary Cyanomercurates NR4+[MHg(CN)4]- with R = Et, Pr; M = Li, Na, K, Cu, obtained by reactions of NR4CN . MCN and Hg(CN)2 in polar solvents, are dimorphous. The low temperature modifications are tetragonal with a space group I4̄, the high temperature forms are cubic with the space group F4̄3m . Reversible phase transitions were studied by DSC, Raman spectroscopy and X-ray diffraction. They are of first order and of displacive character. The X-ray structure determinations of the cubic forms of NEt4MHg(CN)4 with M = Na, Li showed tetra­hedral M (NC)4- and Hg(CN)4- groups connected by linear M -NC -Hg bridges to give three-dimensional frameworks o f a cristobalite type structure and with cavaties, in which the NEt4+ cations are located.

scholarly journals Structural Phase Transitions in [(C2H5)4N]3Sb2Br9 and [(C2H5)4N]3Bi2Br9

1989 ◽  
Vol 44 (11) ◽  
pp. 1102-1106 ◽  
Author(s):  
J. Zaleski ◽  
R. Jakubas ◽  
Z. Galewski ◽  
L. Sobczyk
Keyword(s):  
Phase Transitions ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Electric Permittivity ◽  
X Ray Diffraction ◽  
Reorientational Motion ◽  
X Ray ◽  
First Order ◽  
Dsc Studies ◽  
Permittivity Measurements

Dielectric, DSC and preliminary X-ray diffraction studies on [(C2H5)4N]3Sb2Br9 (TEABA) and [(C2H5)4N]3Bi2Br9 (TEABB) are reported. The compounds are isomorphous, space group P6322. The static electric permittivity measurements on single crystals in the temperature range 220 - 290 K revealed that both compounds show two distinct dielectric anomalies; TEABA at Tc1 = 258 K and Tc2 = 252 K, while TEABB at Tc1= 265 K and Tc2 = 248 K. The DSC studies show only one anomaly of first order at Tc1 =258 K for TEABA, and Tc1 =266 K for TEABB. These transitions are presumably related to a freezing of the reorientational motion of the tetraethylammonium cations

Pressure buffering in a diamond anvil cell

2000 ◽  
Vol 64 (2) ◽  
pp. 241-245 ◽  
Author(s):  
T. Arlt ◽  
R. J. Angel
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Diamond Anvil Cell ◽  
Phase Region ◽  
X Ray Diffraction ◽  
Two Phase ◽  
X Ray ◽  
First Order ◽  
Diamond Anvil ◽  
First Order Phase

AbstractThe clinopyroxenes kanoite and spodumene were studied by single-crystal X-ray diffraction in a diamond anvil cell (DAC) at room temperature. At the displacive phase transitions between the C2/c and P21/c polymorphs both phases coexist within the same crystal. In this two-phase region the pressure in the DAC remains constant. The experimental results demonstrate that pressure buffering at first-order phase transitions can occur in the DAC.

The Application of X-Ray Diffraction at Elevated Temperatures to Study the Mechanism of Formation of Sodium Tripolyphosphate

1961 ◽  
Vol 5 ◽  
pp. 276-284
Author(s):  
E. L. Moore ◽  
J. S. Metcalf
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Amorphous Phase ◽  
Elevated Temperatures ◽  
Sodium Tripolyphosphate ◽  
X Ray Diffraction ◽  
Mechanism Of Formation ◽  
X Ray ◽  
Temperature Form ◽  
High Temperature Form

AbstractHigh-temperature X-ray diffraction techniques were employed to study the condensation reactions which occur when sodium orthophosphates are heated to 380°C. Crystalline Na4P2O7 and an amorphous phase were formed first from an equimolar mixture of Na2HPO4·NaH2PO4 and Na2HPO4 at temperatures above 150°C. Further heating resulted in the formation of Na5P3O10-I (high-temperature form) at the expense of the crystalline Na4P4O7 and amorphous phase. Crystalline Na5P3O10-II (low-temperature form) appears after Na5P3O10-I.Conditions which affect the yield of crystalline Na4P2O7 and amorphous phase as intermediates and their effect on the yield of Na5P3O10 are also presented.

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