Sol–gel synthesis and characterization of xCuO–(1 − x)Bi2O3 (0.15 ≤ x ≤ 0.55) glasses by magnetic and spectral studies

Abstract Binary glasses having compositions xCuO–(1 − x)Bi 2 O 3 (0.15 ≤ x ≤ 0.55) (A1–A5: x:: 0.15, 0.25, 0.35, 0.45, 0.55) are prepared by sol–gel method. Glassy phase is ascertained by powder X-ray diffraction (XRD) studies. Glass transition temperatures, T g , of the glasses are observed to be ~ 573 K. Magnetic studies on the glasses at 300 K in the range ± 10 kG show weak ferromagnetic nature, and additionally the particular glass A3 (x = 0.35) at 5 and 300 K in the range 0–6500 Oe also indicates weak ferromagnetic nature. Observed electron paramagnetic resonance (EPR) lineshapes of the glasses in the range 5–300 K are isotropic in nature, and the corresponding g iso -values ~ 2.1 ± 0.001 are due to similar site symmetries around the Cu 2 + (3d 9 ) ions. Thermally assisted hopping of Cu 2 + (3d 9 ) small polaron modulates the EPR lineshapes which results in motionally narrowed lineshapes. Activation energy of hopping, E a , of the small polaron, calculated from derivative EPR peak-to-peak linewidths of the glasses are observed to be ~ 1 × 10 − 4 eV (~ 10 11 Hz). Broad optical absorption bands ~ 400 nm and ~ 660–735 nm in the glasses are attributed to 2 B 1g → 2 E g and 2 B 1g → 2 B 2g transitions from the ground state 2 B1g (|d x 2 −y 2 >) in Cu 2 + (3d 9 ) ions in tetragonally distorted octahedral environment.