Comparative infrared lattice vibration study of LiGaO₂ and LiInO₂ (I) experimental results

Abstract

Experimental ResultsInfrared reflectivity spectra of LiGaO, and LiInO, samples pressed from powdered niaterial are measured at room temperature in the wavenumber range from 180 to 4000 cm-l. The optical mode frequencies found for LiGaO, agree with measurements on single crystals. I n LiInO, four vibrational modes are found. Comparing the results for LiGaO, and LiInO, some conclusions are made with regard to the Li-0 bond related vibrational modes.Infrarot-Reflexionsspektren von aus pulverformigem Material hergestellten LiGa0,und LiIn0,-Proben wurden bei Raumtemperatur im Wellenzahlbereich von 180 bis 4000 cn-I gemessen. Die fur LiGaO, gefundenen Frequenzen der optischen Moden stimmen mit Messungen an Einkristallen iiberein. I m LiInO, wurden vier optische Modeu gefunden. Aus eineni Vergleich der Ergebnisse fur LiGaO, und LiInO, werden einige SchluBfolgerungen beziiglich der durcli die Li-0-Bindung bedingten Schwingungsmoden gezogen.

Comparative infrared lattice vibration study of LiGaO2 and LiInO2 (II). Interatomic force constants

“…Following the arguments of SOBOTTA et al (1989) this wurtzite-like mode in LiGaO, is ascribed to G a -0 bond vibrations. Experimental and theoretical studies of the lattice vibrations of P-Ga203 support this point of view.…”

“…To solve this problem it has been tentatively assumed that the Li-0 bond related modes have higher frequencies than the G a -0 bond related modes (NEUMANN 1986b), in agreement with the trends observed in LiInS, ), LiInSe, (SOBOTTA et al 1987) and LiInTe, ( K~N et al) exhibiting frequencies of the Li-Cvl bond related modes that are distinctly higher than those of the In-C" bond related modes. However, considering the results of a recent infrared reflectivity study of the lattice vibrations of LiInO, (SOBOTTA et al 1989) and In,O, (SOBOTTA et al 1990) it is obvious that this supposition must be abandoned in the case of the LiB"'0, compounds. In the present work the lattice vibration data of LiGaO, are reconsidered, and revised force constants are proposed for the Li-0 and G a -0 bonds.…”

High‐temperature heat capacity and lattice anharmonicity of LiGaO2

“…Consequently, the relative change of mode frequencies is small, and it can be expected that the temperature variation of the mode frequency can be well represented by a rapidly converging power series expansion in the temperature T. Secondly, it follows from the nonlinear temperature dependence of the thermal expansion coefficient [15] that the mode frequency will also be a nonlinear function of temperature. Then, taking into account that the mode Grüneisen parameters can also depend on temperature the anharmonic contribution to the heat capacity at constant volume becomes In principle, ∆C V (T) can be calculated with (13) provided that all the vibrational mode frequencies ω s (q) and the corresponding mode Grüneisen parameters γ(s,q) are known, for instance from accurate inelastic neutron scattering experiments as a function of pressure and temperature. However, because of the lack of related experimental data for LiGaO 2 further approximations are required.…”

“…Exceptions are the optical modes with lowest frequency [34][35][36][37][38][39][40] and, in particular, the acoustic modes [43][44][45] exhibiting very small and partly negative mode Grüneisen parameters with a pronounced dependence on the wave vector q [44,45]. Therefore, the contribution of these modes to ∆C V (T) can only be calculated using relation (13) with summation over the frequency range from ω = 0 to ω = ω l . However, it has been established experimentally that, within the usual experimental accuracy of heat capacity measurements, anharmonicity effects remain negligibly in the temperature range characteristic of thermal excitation of these modes only [22,46,47].…”

“…The elastic, piezoelectric, dielectric and optical properties of LiGaO 2 have been investigated in detail [8][9][10]. The lattice vibrational characteristics of the compound have also been studied by both infrared reflectivity and Raman scattering measurements on appropriately oriented single crystal specimens [10][11][12][13], and a simple phenomenological force constant model considering interaction between nearest neighbours has been proposed to describe the main trends in the frequencies of the zone-centre optical vibrational modes [14]. However, although anharmonic interactions are expected to play an important role, their influence on the lattice vibrations and on the vibrational thermal properties of the compound has not been investigated in detail so far.…”