Investigating the structural, vibrational, optical, and dielectric properties in Mg-substituted LaAlO3

The structural, vibrational, optical, and dielectric properties have been probed in Mg-substituted LaAlO3. For this purpose, a series of LaAl1-xMgxO3-delta (0 <= x <= 0.20) polycrystalline samples has been prepared using the sol-gel synthesis route. Changes in structural properties due to Mg substitution have been analyzed with the X-ray diffraction technique. The correlation of the degree of distortion of AlO6 octahedra with the E-g and A(1g) modes in Raman spectra has been discussed. Mg substitution leads to decrease the optical bandgap and increases in the electronic disorder in terms of Urbach energy (E-u), which has been investigated using optical absorption spectroscopy. An asymmetry in E-g mode (36 cm(-1)) has been observed in Raman spectra, which could be a signature of electron-phonon interaction induced due to disorder via Mg-substitution. Thus, the role of disorder in the electron-phonon interaction (1/vertical bar q vertical bar) has been understood with the relation between asymmetry parameter (q) of Raman phonon mode and E-u in accordance with an earlier model: I/q(2) proportional to xi E-u + lambda. Further, Impedance spectroscopy has been used to study dielectric response with Mg substitution in LAO. Decrement in the dielectric constant (kappa) has been correlated with the presence of oxygen vacancies and electronic disorder with a relationship E-u proportional to 1/kappa(2).