J. Darul

Vibrational spectra of lithium ferrites: infrared spectroscopic studies of Mn-substituted LiFe5O8 ☆

Abstract Investigations on the series of manganese-substituted lithium ferrites reveal the destructive effect of manganese ions on the ordering of Li+ cations in the spinel-type crystal lattice. A spectacular order–disorder transition with increasing substitution of Mn3+ ions has been observed with infrared spectroscopy, in the region of lattice vibrations. The preference of manganese ions for the octahedral coordination, appears to be associated with the migration of Li+ from octahedral to tetrahedral positions. Results for the LiFe5−yMnyO8 solid solution have been confronted with an order–disorder transition in the pure lithium ferrite.

Synchrotron X-ray powder diffraction studies on the phase transitions in LiMn2O4

Abstract Structural phase transitions of the spinel lithium-manganese oxide, LiMn 2 O 4 ( Fd3m at room temperature) in the temperature range of 300–20 K, were investigated using synchrotron and laboratory X-ray powder diffraction. Splitting of the spinel X-ray lines 311, 400, 440, 531, 533 and 622, recorded during the test, evidenced the reversible formation of cubic, orthorhombic and tetragonal structures. The first transformation starts at ∼290 K as a cubic ( Fd3m )→orthorhombic ( Fddd ) symmetry reduction, and both phases coexist down to 260 K. Below 100 K a second structural transition, orthorhombic→tetragonal ( F4 1 /ddm ) was observed, with the coexistence of these two phases down to ∼40 K. The supercell corresponding to 3 a ×3 a × a ( a , spinel unit-cell constant) has been considered for both orthorhombic and tetragonal polymorphs of LiMn 2 O 4 , based on the appearance of (2.10.0) superstructure X-ray reflection.

High-pressure metaelastic properties of LixMn3−xO4 (x = 0.87, 0.94, 1.00)

High-pressure behaviour of LixMn3−xO4 has been investigated by the in situsynchrotron diffraction method. It has been found that the pressure-induced structural changes lead to the tetragonal phase with c/a > 1 in all materials irrespective of their initial phase. Formation of the tetragonal high-pressure structure is attributed to the Jahn–Teller distortion. The c/a axial ratio increases with the pressure applied for all samples studied. Coexistence of three crystal phases in the transition region has been experimentally confirmed and refinement of their structural parameters has been carried out by the Rietveld method. The effect of the transformation pressure on the pressure medium and the reorientation of MnO6 octahedra have suggested metaelastic character of this transition. Potential applications of the stress-induced transformation in technology of thin-layer batteries have been proposed.

Characterization of chemical and physical parameters of post copper slag

Pilot studies concerning industrial scale application of post copper slag as a nano-additive for the modification of the corrosion resistance of cement composites have been described. The influence of a tribochemical treatment on some physicochemical properties as well as the corrosion resistance of the obtained composites have been evaluated based on DTG, RTG, and SEM coupled with EDX measurements and chemical analysis. It was observed that the so-called “size particle additive effect” influences the course and rate of transformations in the formed cement composites, and may lead to specific and desirable properties.

Hooked on switch: strain-managed cooperative Jahn–Teller effect in Li0.95Mn2.05O4 spinel

The crystal structures, phase equilibria and composition ranges of materials that form lithium–manganese spinels have been studied extensively, frequently to optimize specific properties. Here, we report on the Jahn–Teller switching between two tetragonal structures, which is induced by high pressure. Heating the tetragonal phases under high pressure leads to further transformation to the cubic structure. A transformation of the same type was observed upon heating of Li0.95Mn2.05O4 under ambient pressure, however at a milder temperature. The high-pressure high-temperature experiments were performed under pseudo-hydrostatic conditions at pressures of up to 1.87 GPa and temperatures from 303 to 623 K. Furthermore, the axial ratio of tetragonal phases of Li0.95Mn2.05O4 is analyzed. This pressure/temperature switchable material can exhibit a wide range of novel and manipulable properties.