Full spectrum dielectric response of Bi₂(Zn_1/3Nb_2/3)O₇ thin films in terahertz, infrared and optical frequency regions

Dielectric response of Bi₂(Zn_1/3Nb_2/3)₂O₇, BiZN, thin films was characterized by terahertz (THz), Fourier transform infrared (FTIR) and optical spectroscopies. FTIR measurements reveal the presence of lattice vibrational modes at f₁ = 330 cm^-1 and f₂ = 526 cm^-1. Real part of dielectric constant (ε₁ ≅ 21.5 at f = 200 cm^-1) for the BiZN thin films increases moderately with frequency and drops abruptly at the polarizational resonances corresponding to f₁ and f₂, approaching a low constant value (ε₁ ≅ 2.4-3.6) in high frequency regime (f > 700 cm^-1) High frequency response of BiZN thin films is essentially the same as the dielectric properties measured in optical frequency regime, indicating that there is no lattice vibrational mode beyond 700 cm^-1. The dielectric properties of the films in f > 700 cm^-1 regime is presumably contributed by electronic polarization only. In contrast, the low frequency dielectric constant (ε₁ = 21.5) is still smaller than the ₁-value measured by THz-spectroscopic technique (₁)_THz = 30-38. Such phenomenon infers that there exists additional lattice vibrational mode in between 0.8 and 6 THz (200 cm^-1) frequency regime.