Piezoelectric and pyroelectric properties of BNT-base ternary lead-free ceramic–polymer nanocomposites under different poling conditions

Abstract

Lead-free 0.88(Na_0.5Bi_0.5) TiO₃–0.084(K_0.5Bi_0.5) TiO₃–0.063BaTiO₃ (BNT–BKT–BT) piezoelectric ceramic powders were incorporated into a polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] copolymer matrix to form 0–3 composites. Composites with BNT–BKT–BT volume fraction Ø ranging from 0.10 to 0.40 were fabricated using a hot-press method. These compositions were poled using various procedures to produce three types of samples: one with only the ceramic phase poled; one with polymer and ceramic phases poled in the same direction; and one with the polymer and ceramic phases poled in opposite directions. The effect of the polarisation state on the piezoelectric coefficient d₃₃ and pyroelectric coefficient p of the composite was investigated as a function of the ceramic volume fraction Ø. For the purpose of steadying and compensating the polarization domain, extra free charges were added by the presence of BNT–BKT–BT. In the sample with both ceramic and polymer phases poled in the same direction, the pyroelectric coefficient increased from 26 to 95 μC m⁻² K⁻¹ when the ceramic volume fraction increased from 0–0.20; this is greater than that of the P(VDF-TrFE)-PZT 0–3 composites. In the sample with the phases of the composite film polarised in opposite directions, their piezoelectric activities were reinforced, and d₃₃ was found to increase from 28 to 40 (pC N⁻¹) with a change in ceramic volume fraction ranging between 0 and 30%. One promising usage of the enhanced pyroelectric composites with the ceramic phase and the copolymer phase poled in the same direction is that of sensing components within pyroelectric sensors, while integration in ultrasonic transducer applications is possible in the case of the enhanced piezoelectric composites with the ceramic phase and the copolymer phase poled in opposite directions.