Dongfang Pang

A new (1 − x)Pb(Lu1/2Nb1/2)O3–xPbTiO3 binary ferroelectric crystal system with high Curie temperature

A series of new (1 − x)Pb(Lu1/2Nb1/2)O3–xPbTiO3 (PLN–xPT) binary ferroelectric crystals with high Curie temperature have been successfully obtained firstly by top-seed solution growth technique. A solid-state phase diagram in the low temperature range has been established based on the form of single crystals, which reveals a morphotropic phase boundary (MPB) in the range of 49–51% PT. The polarized light microscope analysis also confirms the coexistence of rhombohedral and tetragonal phase within the MPB. Furthermore, those compositions within MPB exhibit good comprehensive piezoelectric properties. For example, the crystal with composition PLN–0.49PT, showing high Curie temperature Tc = 360 °C and high rhombohedral–tetragonal phase transition temperature TRT = 110 °C, and the piezoelectric coefficient d33, electromechanical coupling coefficient k33, coercive field Ec and remanent polarization Pr are found to be 1630 pC N−1, 81%, 13.8 kV cm−1 and 26.6 μC cm−2, respectively. The large coercive field and high Tc make it a promising candidate for high power transducers in a wider temperature range.

Influence of Mn dopants on the electrical properties of Pb(In0.5Nb0.5)O3–PbTiO3 ferroelectric single crystals

In order to study the influence of Mn doping on the electrical properties of PIN–PT single crystals and develop the materials for high power applications, relaxor-based 0.68Pb(In0.5Nb0.5)O3–0.32Pb(Ti0.92Mn0.08)O3 (Mn-PIN–PT) ferroelectric single crystals with pseudo-cubic symmetry were grown via the conventional flux method. The Mn-PIN–PT crystals have a Curie temperature (TC) of 231 °C and ferroelectric phase transition (TMPB) of 175 °C. Relaxor behavior is identified by the frequency dispersion in dielectric spectra. The piezoelectric coefficient and longitudinal electromechanical coupling factor (k33) are 730 pC N−1 and 80% at room temperature, respectively. The temperature coefficient of k33 is 1.6%, showing good stability up to 180 °C. The ferroelectric properties were measured at different electric fields, showing well-shaped hysteresis loops above 20 kV cm−1. The variation of remnant polarization (Pr), coercive field (EC) and internal bias field (Ei) as a function of temperature was investigated. The Curie temperature and ferroelectric phase transition temperature were decreased and increased, respectively, due to Mn doping, and a typical hard doping effect was confirmed via ferroelectric, dielectric and piezoelectric characterization.

Ferroelectric, piezoelectric properties and thermal expansion of new Bi(Ni3/4W1/4)O3–PbTiO3 solid solutions

Ceramics of the Bi(Ni3/4W1/4)O3–PbTiO3 (BNW–PT) ferroelectric system were synthesized using a conventional solid-state sintering process. A morphotropic phase boundary (MPB) region separating tetragonal and rhombohedral phases has been determined based on X-ray diffraction (XRD) analysis. The composition-dependent phase transition behavior, thermal expansion, di/ferro/piezoelectric properties have been systemically investigated. The volume TECs (thermal expansion coefficients) for 0.1BNW–0.9PT and 0.2BNW–0.8PT are −1.01 × 10−5 per °C and −0.94 × 10−5 per °C, respectively, indicating the negative thermal expansion of some compositions for the binary system. The BNW–PT ceramics have Curie temperatures, TC, ranging from 460 °C to ∼152 °C with the variation of BNW constituent. The tetragonal-rich composition 0.20BNW–0.80PT is found to have the largest remnant polarization, Pr ∼ 23.4 μC cm−2. The highest piezoelectric coefficient d33 ∼ 145 pC N−1 is achieved at MPB composition 0.32BNW–0.68PT. The maximum strain value ∼0.194% is also obtained in the 0.32BNW–0.68PT ceramic.