M. Mączka

Vibrational properties and DFT calculations of the perovskite metal formate framework of [(CH3)2NH2][Ni(HCOO3)] system.

Experimental Raman and IR spectra of multiferroic [(CH3)2NH2][Ni(HCOO)3] were recorded at room temperature. The three-parameter hybrid B3LYP density functional method has been used with the 6-31G(d, p) basis set to derive the equilibrium geometry, atomic spin densities, vibrational wavenumbers, infrared intensities and Raman scattering activities. Based on these calculations, the assignment of the observed bands to the respective internal and lattice modes is proposed. The performed calculations revealed that the ν(NH2) stretching, ρ(NH2) rocking and τ(CH3) torsional modes are very sensitive to formation of the hydrogen bond between the DMA(+) cation and Ni-formate framework. Therefore, these modes are suitable probes for strength of hydrogen bonds in this family of metal-formate frameworks and study of their temperature dependence may provide significant information on a role of the hydrogen bonds in mechanism of the ferroelectric phase transition occurring in these compounds at low temperatures.

A Raman scattering study of pressure-induced phase transitions in nanocrystalline Bi2MoO6

Lattice dynamics calculations and a high-pressure Raman scattering study of nanocrystalline Bi(2)MoO(6), a member of the bismuth-layered Aurivillius family of ferroelectrics, are presented. These studies showed the onset of two reversible second-order or weakly first-order phase transitions near 2.5 and 4.5 GPa as well as some subtle structural changes at 8.2 GPa. Symmetry increases upon application of pressure and the first phase transition involves, most likely, the loss of the MoO(6) tilt mode around a pseudo-tetragonal axis. The second phase transition is associated with the instability of a low wavenumber mode, which behaves as a soft mode. This soft mode most likely corresponds to the polar E(u) mode of the tetragonal I4/mmm aristotype and Bi(2)MoO(6) transforms at 4.5 GPa into the centrosymmetric orthorhombic phase. The sequence of the pressure-induced phase transitions in nanocrystalline Bi(2)MoO(6) is similar to that observed for bulk Bi(2)WO(6) but the critical pressures are significantly lower for the molybdenum compound. Our results also show that the critical pressure of the first phase transition is slightly lower for the nanocrystalline Bi(2)MoO(6) (2.5 GPa) than for the microcrystalline (bulk) Bi(2)MoO(6) (2.8 GPa).

Raman scattering studies of pressure-induced phase transitions in perovskite formates [(CH3)2NH2][Mg(HCOO)3] and [(CH3)2NH2][Cd(HCOO)3].

Pressure-dependent Raman studies were preformed on two dimethylammonium metal formates, [(CH3)2NH2][Mg(HCOO)3] (DMMg) and [(CH3)2NH2][Cd(HCOO)3] (DMCd). They revealed three pressure-induced transitions in the DMMg near 2.2, 4.0 and 5.6 GPa. These transitions are associated with significant distortion of the anionic framework and the phase transition at 5.6 GPa has also great impact on the DMA+ cation. The DMCd undergoes two pressure-induced phase transitions. The first transition occurred between 1.2 and 2.0 GPa and the second one near 3.6 GPa. The first transition leads to subtle structural changes associated with distortion of anionic framework and the later leads to significant distortion of the framework. In contrast to the DMMg, the third transition associated with distortion of DMA+ cation is not observed for the DMCd up to 7.8 GPa. This difference can be most likely associated with larger volume of the cavity occupied by DMA+ cation in the DMCd and thus weaker interactions between anionic framework and DMA+ cations.

Polarised IR and Raman spectra of non-centrosymmetric Na3Li(SeO4)2·6H2O crystal—A new Raman laser material

Polarised IR and Raman spectra of Na3Li(SeO4)2.6H2O single crystal have been recorded. Discussion of the results has been based on the factor group approach for the trigonal R3c (C3v6) space group with Z = 2. The obtained results for the spontaneous Raman scattering have been used in the discussion of the stimulated Raman spectra of the material studied--a new Raman laser crystal.

Temperature-dependent IR and Raman studies of metal–organic frameworks [(CH3)2NH2][M(HCOO)3], M=Mg and Cd

Two metal-organic frameworks of [(CH3)2NH2][M(HCOO)3], where M=Mg and Cd, have been investigated by temperature-dependent IR and Raman methods in order to determine the nature of the phase transition. Our results indicate that phase transition in the Mg-compound is driven by ordering of the dimethylammonium cations. Additional X-ray diffraction and spectroscopic studies on Cd-compound as the function of temperature reveal that this compound does not undergo any structural phase transition. We attribute this behavior to the large size of the cavity occupied by the dimethylammonium cations and thus weak hydrogen bonding between these cations and formate ions.

Dielectric dispersion and Raman spectroscopy in PbHfO3 single crystals modified by addition of Sn ions

Dielectric studies of a PbHf1−xSnxO3 (with x = 0.025) single crystal undergoing two structural phase transformations at about 426 and 474 K were performed in broad frequency and temperature ranges. Phase transitions sequence and their nature were established on the basis of differential scanning calorimetry measurements. Investigations of the complex dielectric permittivity in the frequency range 20 Hz to 2 MHz revealed dipolar dielectric dispersion that exists before AFE2–PE phase transition and is connected with the motion of domain walls. Analysis of temperature evolution of the first-order Raman light scattering spectra confirmed the sequence of phase transitions and gave evidence of locally broken cubic symmetry in the sample due to polar clusters of lower symmetry.

Spectroscopic investigation and DFT modelling studies of Eu 3+ complex with 1-(2,6-dihydroxyphenyl)ethanone

Eu3+ complex with 1-(2,6-dihydroxyphenyl)ethanone in the solid state has been synthesized and characterized by elemental analysis, UV-visible, FT-IR and FT-Raman spectroscopies, powder X-ray diffraction, electron emission under femtosecond laser excitation. The stoichiometry and the formula of the studied complex have been proposed. Its physicochemical properties have been analyzed in terms of the structure and DFT calculations performed for the ligand. The luminescence and dynamics of the excited states depopulation have been studied using femtosecond laser excitation. Spectral and energetic transformation of femtosecond light impulses has been studied and possibility of the energy transfer between the ligand and the Eu3+ electron levels has been analyzed.