Phase transition in
FeTiF6·xH2O·yD2O crystals has been studied by Raman spectroscopy. The 611 cm−1 line corresponding to mode
A1g of
TiF62− system does not exhibit anomalous behavior associated with ...the phase transition. The temperature studies showed that below the phase transition temperature, the equivalence of D2O molecules in
FeTiF6·xH2O·yD2O octahedron is broken. The phase transition mechanism in the compound under study is associated with
Fe(xH2O·yD2O) complex.
The role of iron‐water octahedron in the
FeTiF6·xH2O·yD2O system has been studied by Raman spectroscopy.
A1gTiF62− groups remain stable over the entire temperature range. The main role in phase transition mechanism is due to the transformation of the water complex
Fe(xH2O·yD2O).
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•Raman and optical spectra of disordered hydrated iron fluoridotitanate were studied.•Independent ordering processes of the TiF62− and Fe(H2O)62+ complexes below phase ...transition.•Optical spectra are well interpretable in the Tanabe-Sugano model.•Considerable decrease of inter-electron repulsion in the disordered neighborhood of Fe2+ ions is detected.
Raman and optical absorption spectra of disordered hydrated iron fluoridotitanate (HITF) single crystal were studied. Temperature transformations of the Raman spectra indicate independent ordering processes of the TiF62− and Fe(H2O)62+ complexes below the structural phase transition. The absorption spectrum in the near-infrared and visible ranges includes transitions from the high spin ground state 5T2 of Fe2+ ion to the excited 5E state and a set of excited triplets. Analysis by Tanabe-Sugano method gives crystal field Dq = 490 cm−1 and Racah parameters B = 340 cm−1 and C = 1904 cm−1. Considerable decrease of B parameter as compared to the free ion value indicates a decrease of interelectron repulsion in the disordered neighborhood of Fe2+ ions.
We present the complete genome sequence and proteogenomic map for Acholeplasma laidlawii PG-8A (class Mollicutes, order Acholeplasmatales, family Acholeplasmataceae). The genome of A. laidlawii is ...represented by a single 1,496,992-bp circular chromosome with an average G+C content of 31 mol%. This is the longest genome among the Mollicutes with a known nucleotide sequence. It contains genes of polymerase type I, SOS response, and signal transduction systems, as well as RNA regulatory elements, riboswitches, and T boxes. This demonstrates a significant capability for the regulation of gene expression and mutagenic response to stress. Acholeplasma laidlawii and phytoplasmas are the only Mollicutes known to use the universal genetic code, in which UGA is a stop codon. Within the Mollicutes group, only the sterol-nonrequiring Acholeplasma has the capacity to synthesize saturated fatty acids de novo. Proteomic data were used in the primary annotation of the genome, validating expression of many predicted proteins. We also detected posttranslational modifications of A. laidlawii proteins: phosphorylation and acylation. Seventy-four candidate phosphorylated proteins were found: 16 candidates are proteins unique to A. laidlawii, and 11 of them are surface-anchored or integral membrane proteins, which implies the presence of active signaling pathways. Among 20 acylated proteins, 14 contained palmitic chains, and six contained stearic chains. No residue of linoleic or oleic acid was observed. Acylated proteins were components of mainly sugar and inorganic ion transport systems and were surface-anchored proteins with unknown functions.
In order to clarify ordering mechanisms of ferroic phase transitions in double fluoride salts (NH
4
)
3
SnF
7
, (NH
4
)
3
GeF
7
and (NH
4
)
3
TiF
7
, their Raman scattering spectra have been studied ...in wide ranges of frequencies (20-3400 cm
−1
) and temperatures (8-410 K). Substitution of the central ion in the octahedron groups was found to change not only the phase transition types and sequences, but to modify the types of structural disorder as well, which is a special feature of these high-symmetry fluoride crystals.
Two ammonium oxofluorovanadates, (NH4)3VO2F4 and (NH4)3VOF5, have been investigated by temperature-dependent infrared and Raman spectroscopy methods to determine the nature of phase transitions (PT) ...in these compounds. Dynamics of quasioctahedral groups was simulated within the framework of semi-empirical approach, which justified the cis-conformation of VO2F43− (C2v) and the C4v geometry of VOF53−. The observed infrared and Raman spectra of both compounds at room temperature (RT) revealed the presence at least of two crystallographically independent octahedral groups. The first order PT at elevated temperatures is connected with a complete dynamic disordering of these groups with only single octahedral state. At lower temperatures, the octahedra are ordered and several octahedral states appear. This PT is the most pronounced in the case of (NH4)3VOF5, when at least seven independent VOF53− octahedra are present in the structure below 50K, in accordance with the Raman spectra. Ammonium groups do not take part in PTs at higher and room temperatures but their reorientational motion freezes at lower temperatures.
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•Vibrational spectroscopy is indispensable for study PTs in (NH4)3VO2F4 and (NH4)3VOF5.•The cis-conformation of VO2F43− was justified•From one to seven independent octahedra in the structure of (NH4)3VOF5 during PTs•Ammonium groups are mainly responsible for the PTs at low temperature.
The Raman spectra of four crystals of TbFe
3–
x
Ga
x
(BO
3
)
4
solid solutions (
x
from 0 to 0.54) were studied in the temperature range from 8 to 350 K. The temperatures of structural phase ...transitions were determined. The observed spectral behavior is characteristic to condensation and restoration of soft modes. Soft modes are associated with a structural phase transition from the
R
32 phase to the
P
3
1
21 phase. The Compositions-Temperature phase diagram was constructed.
Magnon mode in α‐MnS Raman spectrum Gerasimova, Julia V.; Abramova, Galina M.; Zhandun, Vyacheslav S. ...
Journal of Raman spectroscopy,
October 2019, 2019-10-00, 20191001, Letnik:
50, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Raman spectra of manganese monosulphide (α‐MnS) with NaCl structure in the temperature range 5–300 К are presented. A new peak at 22 cm–1 has been found at low temperatures. The temperature ...dependence of this peak made possible to attribute it to the magnon mode at k = 0. This is in good agreement with the magnon wavenumber calculated with Munich SPRKKR‐package.
The appearance of a new peak at 22 cm–1 was detected in the Raman spectra of monocrystalline α‐MnS at 5 K that shifts to lower frequencies under heating and disappears at 200 K. Analysis of the observed peak allowed to relate it to the one‐magnon mode associated with magnetic ordering. Calculated frequency of the magnon and the exchange energy estimated with Munich SPRKKR‐package confirms the appearance of this mode to be due to magnetic excitations.
Phase transitions in Rb2KLuF6 crystal Krylov, A. S.; Vtyurin, A. N.; Voronov, V. N. ...
Ferroelectrics,
01/2019, Letnik:
538, Številka:
1
Journal Article
Recenzirano
The Raman spectra of Rb
2
KLuF
6
elpasolite crystal have been studied in a wide temperature range, including two phase transitions: from the cubic phase to the tetragonal phase and then to the ...monoclinic phase. The results of an analysis of the temperature dependences of the parameters of spectral lines are in good agreement with the thermodynamic data on the phase transitions. The analysis of Raman spectra shows that the transition from cubic to tetragonal phase is a second-order transition and the transition from the tetragonal to the monoclinic phase is a weak first-order transition.
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