M. M. Sinha

Vibrational analysis of optical phonons in mixed chromite spinels

Abstract The composition dependence of zone-centre optical phonons of mixed chromite spinel has been investigated. The computational analysis of zone-centre frequencies at all composition ranges lead me to predict one-mode behaviour in these spinels. The present calculation of high-frequency bands in the IR spectrum ( ν 1 and ν 2 ) of the mixed Cu 1− x Mg x Cr 2 O 4 system are in good agreement with experimental results whereas the low frequency ( ν 3 ) differs slightly from observed results. Most of the infrared frequencies of mixed chromite spinels are found nearly insensitive to a modification of the bivalent cations.

A study of the interatomic interaction in oxide spinel MnCr2O4

Abstract The strengths of interatomic interaction in oxide spinel have been investigated by using a short-range force constant model. The interatomic ionic interaction between Cr-O in MnCr2O4 dominates the other interatomic interactions. The zone-centre phonon frequencies thus calculated are found to be in agreement with the observed results.

Study of zone-center phonons in lithium manganese oxide

Abstract The zone-center phonons of spinel structure lithium manganese oxide have been investigated by applying de Launey angular force constant model. The calculation is extended to lithium extracted phases Li 0.5 Mn 2 O 4 and Li 0.015 Mn 2 O 4 also. The lattice phonons thus obtained are compared with available experimental results. The lithiation effects on phonon modes are also discussed.

Study of phonons and normal mode analysis of perovskite-type superionic conductors

Abstract A de Launey angular force (DAF) model has been used to calculate the phonon frequency at zone centre (ZC) and normal modes in phase I of CsPbCl 3 and the γ-phase of Ag 3 SI and Ag 3 SBr by assuming them to be ideal perovskite (P)-type structures. Three central force constants, α 1 , α 2 and α 3 , and three angular force constants, α 1 ′, α 2 ′ and α 3 ′, for Pb–Cl (S–Ag), Cs–Cl (I or Br–Ag) and Cs–Pb (S–I or Br) atoms are employed and determined from the experimental values of transverse infrared (IR) active phonon frequencies at ZC. The α 3 value between Cs and Pb is the strongest among all of these compounds. This is reasonable since both kinds of ions compose the cage lattice in the superionic conduction phase. The normal coordinate of the highest frequency ( ν 1 ) mode is assigned to be different from that for other perovskites. It reasonably interprets the higher values of ν 2 and ν 3 for CsPbCl 3 than those of Ag 3 SX (X=Br,I) and also the lower value of ν 1 for CsPbCl 3 . Based on these results, the complete phonon dispersion curve is calculated.

Lattice vibrations of AVO4 crystals (A = Lu, Yb, Dy, Tb, Ce)

A short range force constant model has been applied using normal coordinates to investigate the Raman and the infrared wavenumbers in rare earth AVO4 compounds (A=Lu, Yb, Dy, Tb, Ce) having space group I41/a and symmetry C4h(6). The calculation of zone center phonons has been made by using four stretching and five bending force constants. The calculated Raman and infrared wavenumbers are in very good agreement with the observed ones. The present calculations interpret reasonably the mode assignment of 779 cm(-1) as Eg mode and 853 cm(-1) as Ag mode in case of LuVO4, which were assigned differently in earlier observation. The potential energy distribution has also been investigated for determining the significance of contribution from each force constant toward the Raman and the infrared wavenumbers.

Zone-centre phonons in spinel structure compounds

Abstract The dependence of the Cr-X force constants, larger than M-X force constants in spinel structure compounds MCr 2 X 4 (M = Mn, Fe, Zn, Hg; X = S, Se), on the structural parameter u has been investigated. An angular force model has been used to study the phonons in these compounds and the inference is drawn that the larger values of the Cr-X force constants are not due to any dependence on the structural parameter but are related to other physical properties of the spinel structure MCr 2 X 4 .

Study of Phonons in Superconducting Oxide Spinels (Li, Mg)1+xTi2–xO4

The lattice dynamics of the spinel phases Li 1+x Ti 2-x O 4 (x = 0, 0.33) has been investigated by applying a de Launey angular force constant model up to third nearest neighbours. The zone centre phonons of superconducting LiTi 2 O 4 and insulating Li 1.33 Ti 1.67 O 4 are compared and analyzed with existing experimental results. The effect on phonons for Mg substituted compounds Li 0.9 Mg 0.1 Ti 2 O 4 and Li 0.7 Mg 0.3 Ti 2 O 4 is also studied and discussed.

Effects of Cl–Cl interaction on phonon dispersion in perovskite type CsPbCl3

Abstract The phonon dispersion curves in three symmetry directions of phase I of CsPbCl 3 superionic conductor are calculated by applying the deLaunay angular force model. With the third neighbor interaction between Cl–Cl ions, considerable agreements are obtained for all phonon frequencies at zone center (ZC) and also for the acoustic modes in the Δ direction. Two high energy phonon modes at ZC-point are reasonably understood.

Lattice dynamics of PbxCd1-xF2 mixed superionic crystals

Abstract A modified rigid ion model has been used to investigate the one-mode behaviour in the PbxCd1-xF2 mixed crystals. It has been found that the said correlation between ionic transport properties and the flourine-cation interaction coefficient for PbxCd1-xF2 crystals is not reasonable. The agreement obtained for the zone centre frequencies with the experiment is satisfactory for all composition range.

Lattice Dynamics of Protonic Conductors AZrO3 (A = Ba, Sr & Pb): A Comparative Study

Recently, many investigations were devoted to the study of family of perovskite-type ABO3 oxides. The material belongs to ABO3 perovskite oxides family like SrZrO3, BaZrO3, PbZrO3 have many characteristics which are suitable for high-voltage and high-reliability capacitor applications. Many acceptor-doped perovskite-type oxides show high protonic conductivity at elevated temperatures. In addition to their reduced temperature operation relative to traditional oxide ion conductors such as Y-stabilized ZrO2, these perovskites, because of their proton transport properties, offer the possibility of application in a number of arenas including hydrogen sensors for molten metals and hydrogen pumps. In this work we are reporting the results of our theoretical investigation on the phonon properties of ABO3 mainly BaZrO3, PbZrO3 & SrZrO3 in cubic phases. The phonon properties are calculated by using lattice dynamical simulation method based on de Launey angular force (DAF) constant model to understand the role of phonon in these systems. The phonon dispersion curves of these proton conductors in cubic phase are also drawn.