Study of new relaxor materials in BaTiO3BaZrO3La2/3TiO3 system
Résumé
Dielectric studies were performed on new lead-free ceramics derived from BaTiO3 by iso-valent and off-valent substitutions in both octahedral and dodecahedral sites and having the compositions (Ba1−xLa2x/3)(Ti1−yZry)O3, with 0 < x < 0.35 and 0 < y < 0.35. The dielectric permittivities of samples measured as a function of temperature and frequency showed relaxor or classical transition phase. The classical ferroelectric behaviour is exhibited by compositions close to the binary systems BaTiO3–La2/3TiO3 (BT–LT) or BaTiO3–BaZrO3 (BT–BZ), as long as the substitution rates remained small (x <0.15 and y <0.30). The relaxor behaviour occurred in compositions BT–LT, BT–BZ and BT–LT–BZ which deviated strongly from BaTiO3. The values of peak temperature TC (or Tm) decreased with increasing x and/or y, being less sensitive to y variations than that of x. In the relaxor zone, the decreasing of Tm is accompanied with an increasing of the characteristic ΔTm, in BT–LT (x < 0.15) and BT–LT–BZ (x = 0.10; 0.05 < y < 0.35) solid solutions. For the best relaxor material of composition (Ba0.90La0.2/3)(Ti0.95Zr0.05)O3, the dielectric constant (ε'r ) and the peak temperature Tm exhibited interesting values (22 000 and 200 K, respectively) if compared to other similar perovskite-like materials. Moreover, such ceramics are lead-free and could fit to environmental friendly requirements in the case of applications.