We have performed both theoretical and experimental study of optical response of parent perovskite manganites RMnO3 with a main goal to elucidate nature of clearly visible optical features. Starting with a simple cluster model approach we addressed the both one-center (p-d ) and two-center (d-d ) charge transfer (CT) transitions, their polarization properties, the role played by structural parameters, orbital mixing, and spin degree of freedom. Optical complex dielectric function of single crystalline samples of RMnO3 (R=La, Pr, Nd, Sm, Eu) was measured by ellipsometric technique at room temperature in the spectral range from 1.0 to 5.0 eV for two light polarizations: E c and E ⊥ c. The comparative analysis of the spectral behavior of ε1 and ε2 is believed to provide a more reliable assignment of spectral features. We have found an overall agreement between experimental spectra and theoretical predictions based on the theory of one-center p-d CT transitions and intersite d-d CT transitions. Our experimental data and theoretical analysis evidence a dual nature of the dielectric gap in nominally stoichiometric matrix of perovskite manganites RMnO3, it is formed by a superposition of forbidden or weak dipole allowed p-d CT transitions and inter-site d-d CT transitions. In fact, the parent perovskite manganites RMnO3 should rather be sorted neither into the CT insulator nor the Mott-Hubbard insulator in the Zaanen, Sawatzky, Allen scheme.

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The optical and magneto-optical properties of ferromagnetic La(1-x)Ba(x)MnO(3) single crystals with x=0.15, 0.20 and 0.25 are studied. The components of the permittivity tensor are obtained by spectral ellipsometry techniques and transverse Kerr effect measurements. The Kerr effect spectra depend substantially on the Ba content. The plasma frequency is estimated. In the paramagnetic semiconductor state, the small polarons contribute to conductivity in La(0.85)Ba(0.15)MnO(3), in La(0.75)Ba(0.25)MnO(3) no evidence for polarons is found even in the semiconductor state. For La(0.85)Ba(0.15)MnO(3) (T(C)=214 K), the metallic phase is estimated to occupy less than 1% of the total volume at T=190 K. It is shown that in La(0.75)Ba(0.25)MnO(3), the energy gap vanishes and the metal-semiconductor transition occurs somewhat below T(C) rather than at T=T(C).

The frequency dependences of the real and imaginary parts of the complex dielectric constant in the spectral range of 0.069 to 5 eV and the temperature dependences of the resistance of the Crloo-xAl, (x 5 32 atyo Al) alloy system are investigated. I n alloys having 16 to 28 atyo of Al, a negative temperature coefficient of resistance, and a minimum metallic conductivity a(0) < < 1000 a-1 cm-l a dielectriza.tion of the optical properties is found characterized by strong anomalous concentration and frequency dependences of the dielectric function in the infrared frequency range. From the analysis of the behaviour of the optical o(w) and the static a(0) conductivities i t is concluded that the anomalies of optical and electrical properties result from the localization of free carriers near the Fermi level. MCCJIenOBaHbI YaCTOTHbIe 3aBHCHM09TH AefiCTBHTeiTbHofi 12 MHHMOfi saCTefi IcOMIlJleKCHO~ AH3JIeKTpPIeCKOa IlpOH12uaeMOCTEI B o 6 n a c~~ CneKTpa 0,069 HO 5 eV M TeMIIepaTypHbIe 3aRHCHMOCTH 3JIeKTpOCOnpOTHBJIeHHR CnJlaBOB CHCTeMbl Crloo-&& (X 5 32 atyo 4). AJIR CIIJIaBOB C 16 80 28 atyo Al, HMeIoWElX OTpHUaTeJlbHbIfi TeMIIepaTypHbIB K 0 3 @ @ H -UEl eHT COlIPOTHBJIeHHR EI MHHHMaJIbHYIo MeTaJlJIH9eCKYKl Il POBOLU4MOCTb O ( 0 ) < 1000 fi-lcm-', 06HapyMeHa HH3JIeHTpH3aq12FI OlITHseCKHX CBOfiCTB, Bblpa3HBlUaRCR B pe3HO aHOMaJIbHOfi EiOH4eHTpa4HOHHOfi H 9aCTOTHOfi 3aBHCHMOCTRX ,qH3JIeKTpH9eCKEIX @lHK4EIfi B HH#pa-IipacHoM ~~a n a s o~e YacToT. H3 a~a~1~3 a nosenemrr onTHsecKoii ~( w ) H cTaTmecrcot o(0) nposonmMocTefi AenaeTcR ~~K J I I O~~H H~, YTO aHoMamwi on'rmecmix II ~J I~K T~H Y~C K H X CBOfiCTB BbI3BaHbI JlOHaJI123aUHe~ CBO6OAHbIij[ HOcHTenefi ~6 .~1 1 2 3~ YPOBHR QepMH.