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The morphotropic phase boundary (MPB) of PbMg1/3Nb2/3O3-xPbTiO3 (PMN-xPT) and its derivatives has been reported to exhibit a giant piezoelectric coefficient (d33). Hence, it is essential to understand the origin of excellent piezoelectric properties. In the present work, we observed that the cubic–tetragonal–rhombohedral triple point in the phase diagram of the PMN-xPT system is itself a critical point. The criticality of the triple point is evidenced by the nearly zero transition thermal hysteresis, the maximized dielectric permittivity, and the largest degree of elastic softening. The Landau modeling calculations reveal that such a critical triple point exhibits infinitely high piezoelectricity, which explains the origin of the giant piezoelectricity of the PMN-xPT system. This work illustrates that the near-criticality of the MPB composition is inherited from the criticality of the triple point. This study would stimulate work on searching materials with high piezoelectricity by designing a critical triple point. [ABSTRACT FROM AUTHOR]

The investigation of fine structural evolutions around the morphotropic phase boundary (MPB) is important to understand the origin of the high piezoelectricity in ferroelectric ceramics. Here, we report a new phase boundary associated with oxygen octahedral tilt–untilt transition by exploring average and local structural evolutions in the vicinity of MPB in Bi0.5Na0.5TiO3–PbTiO3 (BNT–PT) ceramics. It is found that the local structural change of the oxygen octahedral tilt–untilt transition is decoupled with the average structural change of the rhombohedral-to-tetragonal phase transition at MPB in BNT–PT. The slight octahedral tilting distortion at MPB is responsible for the large high-field-induced electrostrain and small low-field-induced piezoelectricity in BNT–PT. The crucial difference of MPB between BNT–PT and the classical piezoelectric Pb(Zr,Ti)O3 is discussed from their local structural evolutions of octahedral tilting to the performance changes at MPB. It helps us to figure out the origin of large high-field-induced electrostrain but small piezoelectricity in BNT-based ceramics. [ABSTRACT FROM AUTHOR]

Multiferroic composites of (1-x)GaFeO3-(x)Co0.5Zn0.5Fe2O4 with x = 0.0, 0.1, 0.2, and 1 were prepared using a conventional solid state reaction method. The X-ray diffraction patterns confirmed that the composites consisted of cubic spinel Co0.5Zn0.5Fe2O4 and orthorhombic GaFeO3 phases. The coexistence of both magnetic and ferroelectric orderings at ambient temperature was confirmed by measuring M-H and P-E loops. The inclusion of Co0.5Zn0.5Fe2O4 enhanced magnetization and dielectric constant, as well as improved the ferroelectric properties of GaFeO3. The leakage current (9.33 × 10−8 A/cm2) of composite (x = 0.20) is found to be much lower as compared to pure GaFeO3. The value of saturation magnetization increased to 30.6 emu/g at 300 K. This large enhancement of magnetization, as well as the presence of ferroelectricity, is promising for enabling future magnetoelectric applications. [ABSTRACT FROM AUTHOR]

For more than half a century, the morphotropic phase boundary (MPB) has drawn constant interest in developing piezoelectric materials, as the phase instability at the region significantly enhances piezoelectricity. However, the local structure/symmetry at the MPB region is still under controversy. The investigation on morphology and origin of the local structure at MPB is of considerable importance to provide a microstructure basis for high piezoelectricity. In the present study, we thus use high resolution transmission electron microscopy to investigate the microstructure feature of MPB at PMN-PT ceramics. The local structure is shown to be the coexistence of nano-scaled {110}-type rhombohedral (R) twin and {110}-type tetragonal (T) twin. Such nano-scaled coexistence can be due to a nearly vanishing polarization anisotropy and low domain wall energy at MPB, which thus facilitates polarization rotation between <001>T and <111>R states and leads to high properties of MPB compositions. [ABSTRACT FROM AUTHOR]

The stabilization effect, an increase of the reverse transition temperature TC with ferroelectric aging time, was recently found in acceptor doped ferroelectrics. Such an effect has found a microscopic explanation in the symmetry-conforming principle of point defects, which also accounts for a similar stabilization effect in ferroelastic/martensite materials. However, such a microscopic model is difficult to use to make a quantitative/semiquantitative evaluation of the aging process. In the present work, we propose a single-domain thermodynamic model that provides a semiquantitative fit to the experimentally observed stabilization kinetics. Furthermore, it predicts a new aspect of ferroelectric aging: the decrease of latent heat ΔH of the reverse transition with aging time. Such a prediction was confirmed via experimental differential scanning calorimetry results. [ABSTRACT FROM AUTHOR]