La Substitution into the Melilite Derivative CaGaO: Prediction, Synthesis and Ionic Conductivity.

Melilite-type gallates of general formula REAEGaO are of interest for their ability to host mobile interstitial oxide ions in [GaO] layers. The crystal structure of CaGaO is closely related to melilite, with [GaO] layers stacked in a more complex way to accommodate an additional 0.5 interlayer cations per formula unit, suggesting the potential for similar oxide ion conduction behavior.

An study of thermal crystallization of amorphous calcium phosphates.

The heat-induced crystallization of amorphous calcium phosphate (ACP) is an intriguing process not yet well comprehended. This is because most of the works on this topic are based on studies where the materials are characterized after the heat and cooldown cycles, thus missing transient structural changes. Here, we used time-resolved energy dispersive X-ray diffraction and infrared spectroscopy to study, for the first time, the thermal crystallization of ACP .

Infrared spectroscopy of CeO nanoparticles using Bergman's spectral representation: effects of phonon confinement and lattice strain.

The dielectric function of a cerium oxide nanopowder has been investigated by infrared spectroscopy. The use of Bergman's spectral representation and a semi-quantum dielectric function model allows an accurate retrieval of the main features of the lattice dynamics of this nanocompound. Due to the absence of significant lattice strain or vacancy concentration, the observed differences between the dielectric functions of the nanopowder and a single crystal can be explained mainly by the phenomenon of phonon confinement.

Accessing New Charge-Transfer Complexes by Mechanochemistry: A Tetrathiafulvalene Chloranilic Acid Polymorph Containing Segregated Tetrathiafulvalene Stacks.

Two polymorphs of tetrathiafulvalene chloranilic acid (TTF-CAH) have been synthesized by mechanochemistry. The previously known "ionic" polymorph (form I) was prepared by liquid-assisted grinding (LAG) using various highly polar solvents as well as protic but moderately polar solvents, such as alcohols of one to four carbon atoms. A new TTF-CAH polymorph (form II) was obtained by LAG and slurry mechanochemistry using aprotic, low-polarity solvents, as well as nonpolar solvents and neat grinding.

Phonons and hybrid modes in the high and low temperature far infrared dynamics of hexagonal TmMnO3.

We report on temperature dependent TmMnO3 far infrared emissivity and reflectivity spectra from 1910 K to 4 K. At the highest temperature the number of infrared bands is lower than that predicted for centrosymmetric P63/mmc (D(4)(6h)) (Z = 2) space group due to high temperature anharmonicity and possible defect induced bitetrahedra misalignments. On cooling, at ~1600 ± 40 K, TmMnO3 goes from non-polar to an antiferroelectric-ferroelectric polar phase reaching the ferroelectric onset at ~700 K.

Paramagnetic collective electronic mode and low temperature hybrid modes in the far infrared dynamics of orthorhombic NdMnO₃.

We report on the far- and mid-infrared reflectivity of NdMnO3 from 4 to 300 K. Two main features are distinguished in the infrared spectra: active phonons in agreement with expectations for the orthorhombic [Formula: see text]-Pbnm (Z = 4) space group remaining constant down to 4 K and a well defined collective excitation in the THz region due to eg electrons in a d-orbital fluctuating environment. We trace its origin to the NdMnO3 high-temperature orbital disordered intermediate phase not being totally dynamically quenched at lower temperatures.

High temperature far-infrared dynamics of orthorhombic NdMnO3: emissivity and reflectivity.

We report on near normal far- and mid-infrared emission and reflectivity of NdMnO3 perovskite from room temperature to sample decomposition above 1800 K. At 300 K the number of infrared active phonons is in close agreement with the 25 calculated for the orthorhombic D(2h)(16)-Pbnm (Z = 4) space group. Their number gradually decreases as we approach the temperature of orbital disorder at ~1023 K where the orthorhombic O' lower temperature cooperative phase coexists with the cubic orthorhombic O.

Collective phase-like mode and the role of lattice distortions at TN ~TC in RMn2O5 (R= Pr, Sm, Gd, Tb, Bi).

We report on electronic collective excitations in RMn(2)O(5) (R =Pr, Sm, Gd, Tb) showing condensation starting at and below ~T(N) ~T(C)~ 40-50 K. Their origin is understood as partial delocalized e(g) electron orbitals in the Jahn-Teller distortion of the pyramid dimer with strong hybridized Mn(3+)-O bonds. Our local probes, Raman, infrared, and x-ray absorption, back the conclusion that there is no structural phase transition at T(N)~T(C).