Infrared Study of Surface Vibration Modes in MgO Small Cubes

The infrared transmission spectra of MgO small cubes were measured over a wide range of the dielectric constant of surrounding medium. The results were analysed on the basis of the theory of surface normal modes in cubic particles. Observed shift of the main-absorption peak (located between the bulk-phonon frequencies ω T and ω L ) with respect to the dielectric constant of surrounding medium is in close agreement with the theoretical prediction. The position and shape of experimental curves of absorption coefficients can be reproduced fairly well by the theory of cubes. In addition, one type of the samples showed the absorption peak at ω T , which is interpreted as due to the formation of particle chains, while the other type did not show the absorption peak due to the separation of particles from each other.