Infrared-active phonons of perovskite HoMn1-xCoxO3 (x=0--0.8)

Polycrystalline perovskites compounds HoMn_1-xCo_xO₃ (x=0--0.8) have been prepared by conventional solid-state reaction. Here, we used far-infrared (FIR) spectroscopy to study infrared active phonon modes and present a comparative analysis of infrared transmission spectra of polycrystalline HoMn_1-xCo_xO₃ (x=0--0.8). The data indicated that phonon modes significantly changed with increase of cobalt doping level. Four main bands were assigned as external, torsional, bending and stretching bands. The external vibration energy remain same at ω₁∼190 cm^-1 for Co doping x≤0.5 and shift to higher energy for x>0.5. Torsional and bending bands exhibit splitting. The stretching band is at 600 cm^-1 for all samples, but the bandwidth is reduced as Co doping increased. The transmission spectrum of HoMn₄5/Co₁5/O₃ was analyzed to obtain the spectrum of optical density. The minimum number of oscillators to obtain a reliable fit is 5 by using a sum of noninteracting harmonic oscillators.