Phase distribution and corresponding piezoelectric responses in a morphotropic phase boundary Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal revealed by confocal Raman spectroscopy and piezo-response force microscopy

Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) single crystals exhibit ultrahigh piezoelectric property and have already been applied in various industrial fields. Here, spatial distribution of coexistent phases and corresponding local piezoelectric responses in a morphotropic phase boundary (MPB) PMN-xPT single crystal are thoroughly investigated by confocal Raman spectroscopy coupled with piezo-response force microscopy (PFM). Different from previous studies on MPB crystals, spatial distribution of coexistent phases is exhibited intuitively in an image obtained by confocal Raman mapping. Via in-situ PFM measurements, domain morphology of each coexistent phase is observed. Moreover, local piezoelectric responses of each coexistent phase are obtained by switching spectroscopy PFM measurements, indicating that Ma and Mc phases behave like PNRs and polar matrix in PMN-xPT crystals Our work clarifies the contribution from different phases to the giant piezoelectric performance, which can deepen the understanding on the ultrahigh piezoelectricity in PMN-xPT crystals and provide the key point for developing novel high piezoelectricity materials.     

Preparation,structure, and electric properties of the Pb(Zn1/3Nb2/3)O3–Pb(Yb1/2Nb1/2)O3–PbTiO3 ternary ferroelectric system ceramics near the morphotropic phase boundary

Ceramics of the xPb(Zn_1/3Nb_2/3)O₃–(1 ? x ? y)Pb(Yb_1/2Nb_1/2)O₃–yPbTiO₃ (PZN–PYN–PT) ternary system were synthesized using a modified two-step columbite precursor method which can effectively suppress the pyrochlore phase. A morphotropic phase boundary (MPB) region, separating tetragonal and rhombohedral phases in the ternary systems has been determined. The electric properties of the compositions near MPB region were investigated. Dielectric response exhibits relaxor-like characteristics with broad dielectric peaks and dispersive dielectric behavior with respect to frequency and temperature. The phase diagram of the 0.45PZN–(0.55 ? y)PYN–yPT pseudo-binary system in the composition range of 0.15 < y < 0.35 was established based on dielectric measurements. The optimal properties were achieved in the MPB composition of 0.52PZN–0.21PYN–0.27PT with piezoelectric coefficient d₃₃, dielectric permittivity ε′, planar electromechanical coupling k_p, dielectric loss tan δ, coercive field E_c, remnant polarization P_r, and T_C being of 558 pC/N, 2065, 62%, 0.2%, 19.88 kV/cm, 31.44 μC/cm² and 259.5 °C, respectively, showing potential usage in high-temperature electromechanical applications.     

Large electrocaloric strength in the (100)-oriented relaxor ferroelectric Pb[(Ni1/3Nb2/3)0.6Ti0.4]O3 single crystal at near morphotropic phase boundary

Relaxor ferroelectric Pb[(Ni_1/3Nb_2/3)_0.6Ti_0.4]O₃ (PNNT) single crystal with composition close to the morphotropic phase boundary (MPB) was successfully prepared using the molten salt method. The analysis results of XRD and TEM indicated that the as-grown crystal is of almost pure perovskite phase with coexistence of tetragonal and rhombohedral. Typical relaxor behavior was observed when the crystal was aged. Large electrocaloric strength (ΔT/ΔE) of 44.97 mK cm/kV was obtained near the phase transition temperature of paraelectric to ferroelectric, indicating that PNNT is a promising material for application in cooling system. Moreover, it is found that the aging of point defects may make an important contribution to the electrocaloric performance of the single crystal, in addition to the contribution of the transition of phases induced by the electric field.     

Anisotropic domain structures of Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 single crystals with high ferroelectric phase transition temperature

The anisotropic domain structures and local piezoresponse of rhombohedral Pb(Mg_1/3Nb_2/3)O₃–PbZrO₃–PbTiO₃ single crystals with high ferroelectric phase transition temperature (T_FE‐FE≥120°C) were systematically investigated by vector piezoresponse force microscopy. The typical size of labyrinthine domain pattern for [001]_C sample was in the range of 100‐200 nm, revealing its relaxor feature. While the [011]_C sample exhibited ordered ribbon‐shaped domain pattern with preferential alignment along <011> direction since the modulation effect of polar nanoregions. For [111]_C sample, it had messy and featureless domain patterns. For as‐grown crystal, the incorporation of Zr⁴⁺ cation in Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ system resulted in that the long‐range coulomb interactions of the charged ions in the short range order regions were weakened, leading to an increased relaxor feature. Concurrently, the incorporation of Zr⁴⁺ cation enhanced the Pb‐B repulsion intensity, resulting in an improved T_FE‐FE. Temperature‐dependent properties of as‐grown crystal exhibited good temperature stability from 30 to 120°C, indicating it is a promising material for actuator and ultrasonic transducer applications.     

Two–step processing of thermoelectric (Ca0.9Ag0.1)3Co4O9/nano–sized Ag composites with high ZT

A two–step processing method, spark plasma sintering (SPS) combined with a heat–treatment, was used to fabricate (Ca_0.9Ag_0.1)₃Co₄O₉/nano–sized Ag composites. Sliver within the lattice generated hole carriers, and silver along the grain boundaries improved the transport path of the charge carriers. Samples sintered using SPS at different temperatures had very different thermoelectric properties. The results showed that when the sample was sintered at 1233 K, the maximum power factor reached 0.43 mW/(m·K²) along with an electrical resistivity of 8.61 mΩ·cm and a Seebeck coefficient of 196.90 μV/K, and the corresponding lattice thermal conductivity was 1.86 W/(m·K). This study shows how to improve the properties and broaden the application of Ca₃Co₄O₉ thermoelectric ceramics.