Enhanced piezoelectric properties in LixBi1-xNbxFe1-xO3 films contributed by low-symmetry phase and self-polarization

Abstract

LixBi1-xNbxFe1-xO3 films with various Li+ and Nb5+ substitutions were fabricated onto LaNiO3-buffered Pt(111)/Ti/SiO2/Si substrates through sol-gel methods. Owing to the substitution by smaller Li+ and Nb5+ for larger Bi3+ and Fe3+ respectively, the phase structure of LixBi1-xNbxFe1-xO3 films experiences a transition from rhombohedral phase (R phase, high symmetry) to tetragonal-like phase (T-like, low-symmetry) upon the chemical pressure with Li+ and Nb5+ substitution increases. Additionally, the dielectricity, ferroelectricity and leakage behaviors of substituted LixBi1-xNbxFe1-xO3 films are also significantly improved. More importantly, the substituted LixBi1-xNbxFe1-xO3 films show significantly enhanced piezoelectric responses, especially for the Li0.05Bi0.95Nb0.05Fe0.95O3 film, whose d33 with the value of 107.5 pm/V might be compared with some lead-based piezoelectric films. The enhanced piezoelectric response of the Li0.05Bi0.95Nb0.05Fe0.95O3 film is contributed by synergistic effects of low-symmetry phase, improved ferroelectricity and downward self-polarization, where the electric field-triggered R-T phase transition and polarization vectors rotation can be easily took place upon small stimuli. Additionally, the reduction of leakage currents for substituted LixBi1-xNbxFe1-xO3 films also help to improve their dielectric, ferroelectric and piezoelectric properties.