Phase coexistence and the magnetic glass-like phase associated with the Morin type spin reorientation phase transition in SmCrO3

RSC Advances ◽  
2016 ◽  
Vol 6 (93) ◽  
pp. 90255-90262 ◽  
Author(s):  
Malvika Tripathi ◽  
R. J. Choudhary ◽  
D. M. Phase
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Phase Coexistence ◽  
Spin Reorientation ◽  
Reorientation Process ◽  
Magnetic Glass

SmCrO3 undergoes a discontinuous Morin type spin reorientation process due to discrete flipping of Cr3+ ions from the high temperature Γ4 to low temperature Γ1 configuration.

Mössbauer Studies of Fe2+ in Iron Langbeinites and other Crystals with Langbeinite Structure

1998 ◽  
Vol 53 (1-2) ◽  
pp. 27-37 ◽  
Author(s):  
M. Windhaus ◽  
B. D. Mosel ◽  
W. Müller-Warmuth
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Low Temperature ◽  
High Spin State ◽  
Cubic Phases ◽  
Debye Temperatures ◽  
Phase Transition Temperatures ◽  
Abrupt Changes ◽  
Temperature Dependences

Abstract 57 Fe Mössbauer spectra have been measured at various temperatures between 4.2 K and 300 K for iron langbeinites A 2 Fe 2^04)3 with A = K, NH 4 , Rb, T1 and magnesium, manganese and cadmium lang-beinites doped with Fe" + . The spectra revealed several contributions whose isomer shifts and quadru-pole splittings have been obtained by fitting program routines. For the high-temperature cubic phases two crystallographically non-equivalent iron sites have been identified, characteristic of Fe2+ in the high-spin state. Abrupt changes of the quadrupole couplings indicated phase transitions; in some cases, the spectra have also revealed several sites for Fe2+ in low temperature phases. From the temperature dependences, phase transition temperatures, crystal field splittings and Debye temperatures have been derived.

35Cl NQR Studies of Hexachlorometallates(IV) with Organic Cations, A2 [MCl6] and A'[MCl6], M=Sn, Te, Pb and A+, A'2+ = Organic Cation

1990 ◽  
Vol 45 (3-4) ◽  
pp. 293-302 ◽  
Author(s):  
Dirk Borchers ◽  
Alarich Weiss
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Resonance Line ◽  
Organic Cation ◽  
Phase Changes ◽  
Organic Cations ◽  
Temperature Phase ◽  
35Cl Nqr ◽  
Low Temperature Phase

Abstract35Cl NQR spectra of eleven hexachlorometallates (IV) A1 [MCl6] and A'[MCl6], M = Sn, Te, Pb, and A+ =ethylammonium, 4-picolinium, anilinium, triethylammonium, chinoxalinium, and piperi-dinium ions, and A'2+ = 1.3-propylenediammonium ion, have been observed as a function of tem-perature. The ethylammonium hexachlorometallates(IV) (C2H5 NH3)2 [MCl6], M = Sn, Te, show a phase transition at 128.8 K and 204 K, respectively. Both compounds yield a single resonance line in their high temperature phases. In case of the stannate this single 35Cl resonance line splits up into two lines at Tc = 128.8 K, whereas for the tellurate no 35Cl NQR signals could be found in the low temperature phase. A phase transition was also found for the 1.3-propylenediammonium hexa-chlorostannate(IV) at 287 K where the six line NQR spectrum of the low temperature phase changes into a four line spectrum. In contrast, the corresponding plumbate shows no transition. All other compounds studied contain distorted [MCl6]2- octahedra, and therefore they yield more than one 35Cl resonance line. The complexes have been investigated in the temperature range temperature where the lines fade out. In case of the hexachlorostannates(IV) with the ethylammonium, the 1.3-propylenediammonium and the triethylammonium ions, the crystal structures of the compounds are known and compared with the results of the 35Cl NQR spectroscopy.

Phase transitions in solid cycloheptene

1990 ◽  
Vol 68 (4) ◽  
pp. 604-611 ◽  
Author(s):  
Julian Haines ◽  
D. F. R. Gilson
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
Low Temperature Phase

The phase transition behaviour of cycloheptene has been investigated by differential scanning calorimetry, proton spin-lattice relaxation, and vibrational spectroscopy (infrared and Raman). Two solid–solid phase transitions were observed, at 154 and 210 K, with transition enthalpies and entropies of 5.28 and 0.71 kJ mol−1 and 34.3 and 3.4 JK−1, respectively. Cycloheptene melted at 217 K with an entropy of melting of 4.5 JK−1 mol−1. The bands in the vibrational spectra of the two high temperature phases were broad and featureless, characteristic of highly disordered phases. The presence of other conformers, in addition to the chair form, was indicated from bands in the spectra. The ring inversion mode was highly phase dependent and exhibited soft mode type behaviour prior to the transition from the low temperature phase. The low frequency Raman spectra (external modes) of these phases indicated that the molecules are undergoing isotropic reorientation. In the low temperature phase, the vibrational bands were narrow; the splitting of the fundamentals into two components and the presence of nine external modes are consistent with unit cell symmetry of either C2 or Cs with two molecules per primitive unit cell. A glassy state can be produced from the intermediate phase and the vibrational spectra were very similar to those of the high temperature phases, indicating that static disorder was present. The barriers to reorientation, as obtained from proton spin-lattice relaxation measurements, are 9.0 kJ mol−1 in both the high temperature phases, and 15.4 kJ mol−1 in the low temperature, ordered phase. Keywords: cycloheptene, phase transition, differential scanning calorimetry, NMR, vibrational spectroscopy.

scholarly journals The phase transition of rubidium hydrogen carbonate, RbHCO3

2017 ◽  
Vol 73 (7) ◽  
pp. 975-979 ◽  
Author(s):  
Carla Larvor ◽  
Berthold Stöger
Keyword(s):  
Phase Transition ◽  
Hydrogen Bonding ◽  
High Temperature ◽  
Hydrogen Atom ◽  
Low Temperature ◽  
Three Dimensional ◽  
Disorder Phase Transition ◽  
Dimensional Network ◽  
Hydrogen Carbonate ◽  
Index 2

Rubidium hydrogen carbonate, RbHCO3, features an order/disorder phase transition atTC= 245 K from the high-temperature (HT) disorderedC2/mmodification to the low-temperature (LT)C-1 modification. The crystal structures are characterized by [HCO3]22−pairs of hydrogen carbonate groups connected by strong hydrogen bonding. The [HCO3]22−pairs are connected by Rb+cations into a three-dimensional network. In HT-RbHCO3, the hydrogen atom is disordered. In LT-RbHCO3, ordering of the hydrogen atom leads to atranslationengleichesymmetry reduction of index 2. The lost reflections and rotations are retained as twin operations.

Vibrational Spectra of N2H5HC2O4 and N2D5DC2O4

1975 ◽  
Vol 53 (9) ◽  
pp. 1387-1392 ◽  
Author(s):  
R. Savoie ◽  
M. Guay
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Crystal Structures ◽  
Raman Spectra ◽  
Vibrational Spectra ◽  
Unit Cell ◽  
Infrared And Raman Spectra ◽  
Solid Phases ◽  
High Temperature Modification

Infrared and Raman spectra of N2H5HC2O4 and N2D5DC2O4 have been recorded at various temperatures between 77 and 300 K. The results at 300 K are consistent with the known crystal structures of these solids. A phase transition has been detected at ∼ 240 K in N2D5DC2O4 and although there are similarities between the two stable solid phases of this compound, the low-temperature form appears to be centrosymmetric and to have a larger unit cell than the high-temperature modification.

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