Jian Zhuang

Local polar structure and multiferroic properties of (1−x)Bi0.9Dy0.1FeO3−xPbTiO3 solid solution

The multiferroic (1–x)[0.9BiFeO3–0.1DyFeO3]–xPbTiO3 (BDF–xPT) solid solution with compositions around the morphotropic phase boundary (x = 0.25, 0.28, 0.31, 0.34, and 0.37) has been synthesized in the form of ceramics. The phase symmetry, microstructure, ferroelectricity, piezoresponse, and ferromagnetic properties have been characterized by various techniques. It is found that, with increasing content of lead titanate from x = 0.25 to x = 0.37, the grain size increases and the ferroelectric property is improved. The ferroelectric performance is further enhanced by the introduction of an excess amount (2%) of TiO2 or by sintering in oxygen atmosphere, which reduces the leakage. The local polar structure is imaged by piezoresponse force microscopy. Both the out-of-plane and in-plane images reveal distinct ferroelectric domain structures, with the amplitude and the average domain size decreasing with the increase of lead titanate amount. Compared with the (1–x)BiFeO3–xPbTiO3 binary solid solution of about the same concentration of PT, the magnetic properties are enhanced in BDF–xPT due to the presence of dysprosium, as demonstrated by the ferromagnetic hysteresis loops displayed at room temperature and at 10 K, but the remnant magnetization decreases with increasing PT content. The simultaneous presence of ferroelectricity and ferromagnetism entitles the BDF–xPT solid solution a room-temperature multiferroic material.

Structure and local polar domains of Dy-modified BiFeO3–PbTiO3 multiferroic solid solutions

To investigate the effects of dysprosium ions on the crystal structure and multiferroic properties of the bismuth ferrite-based systems, Dy-substituted solid solutions of 0.66Bi1−xDyxFeO3–0.34PbTiO3, with x = 0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4 and 0.5, have been synthesized and characterized. With increasing concentration of Dy, the crystal structure transforms from a primarily tetragonal P4mm phase to a rhombohedral R3c phase. Moreover, the R3c (or monoclinic Cc) phase is found to coexist with the P4mm phase in the composition range of 0 ≤ x < 0.2, which is attributed to the effect of Dy that favours the rhombohedral structure. Interestingly, the ferroelectric phase transition temperature TC increases with increasing Dy concentration for compositions with x ≥ 0.1. This is explained by the crystal structural effect that compensates the dilution effect of ferroelectrically active Bi3+. Piezoresponse force microscopy (PFM) imaging reveals the formation of 180° polar domains, which can be switched by applying electric fields through the PFM tip, confirming the ferroelectricity. A partial phase diagram is established in terms of composition and temperature. It describes the crystal structure and ferroelectric phases, as well as the solubility limit, of the Bi1−xDyxFeO3–PbTiO3 solid solution system.

Magnetoelectric relaxor and reentrant behaviours in multiferroic Pb(Fe2/3W1/3)O3 crystal.

Significant quenched disorder in crystal structure can break ferroic (magnetic or electric) long-range order, resulting in the development of ferroic glassy states at low temperatures such as magnetic spin glasses, electric dipolar glasses, relaxor ferroelectrics, etc. These states have been widely studied due to novel physical phenomena they reveal. Much less known are the effects of quenched disorder in multiferroics, i.e. the materials where magnetic and electric correlations coexist. Here we report an unusual behaviour in complex perovskite Pb(Fe2/3W1/3)O3 (PFW) crystals: the coexistence of electric relaxor, magnetic relaxor and antiferromagnetic (AFM) states. The most striking finding is the transformation of the AFM phase into a new reentrant-type magnetic glassy phase below Tg ≅ 10 K. We show that the behaviour at this transformation contrasts the typical behaviour of canonical spin glasses and is similar to the behaviour of relaxor ferroelectrics. Magnetoelectric effect is also observed in the AFM phase in the temperature range of the transition into electric relaxor phase at Tf ≅ 200. The mechanism of magnetic relaxor behaviour is supposed to arise from the frustrated interactions among the spins located at the AFM domain walls. Our results should inspire further studies of multirelaxor behaviour in other multiferroic systems.

Piezoresponse and magnetic properties of multiferroic (1−x)Bi0.9Dy0.1FeO3–xPbTiO3 solid solution

The multiferroic solid solution of (1−x)[0.9BiFeO3–0.1DyFeO3]–xPbTiO3 with compositions around the morphotropic phase boundary has been synthesized in the form of ceramics and characterized by Piezoresponse Force Microscope (PFM) and Superconducting Quantum Interference Device. Both the original local polar domain structure and the domain evolution after poling have been studied by PFM. The PFM phase imaging has revealed some interesting details of poling and domain switching process: The out-of-plane phase image shows a uniform direction of polarization along the applied electric field, while the in-plane phase image indicates two kinds of domains with antiparallel polarizations. This kind of poled domain structure is explained based on the orientations of the polarization as permitted by the rhombohedral crystal symmetry in grains of different crystallographic orientations. The magnetic properties measured within the temperature range from 1.8 K to 300 K reveal an interesting sequence of magnetic transi...

Coexisting ferroelectric and magnetic morphotropic phase boundaries in Dy-modified BiFeO3-PbTiO3 multiferroics

Morphotropic phase boundary (MPB) in ferroelectric solid solutions can significantly enhance the dielectric and piezoelectric performances of the materials. Similarly, magnetic MPB has been found to exist in a few ferromagnets and is proved to be greatly beneficial to the magnetostrictive response. In this letter, we report the finding of a magnetic MPB in the multiferroic 0.66Bi1−xDyxFeO3-0.34PbTiO3 system, which overlaps the structural MPB of ferroelectric phases. A (weak) ferromagnetic state is induced at room temperature by Dy for the rhombohedral compositions with x ≥ 0.10. Upon cooling down from room temperature, the tetragonal compositions (x ≤ 0.05) show only one magnetic phase transition from the paramagnetic to antiferromagnetic phase, while the rhombohedral compositions exhibit a series of magnetic phase transitions from the (weak) ferromagnetic state to an antiferromagnetic order then to another weak ferromagnetic phase. A magneto-structural phase diagram has been established that reveals the ...

Correction: Structure and local polar domains of Dy-modified BiFeO3–PbTiO3 multiferroic solid solutions

Correction for ‘Structure and local polar domains of Dy-modified BiFeO3–PbTiO3 multiferroic solid solutions’ by Jian Zhuang et al., J. Mater. Chem. C, 2015, 3, 12450–12456.

Novel ferroelectric single crystals of Bi(Zn1/2Ti1/2)O3-PbZrO3-PbTiO3 ternary solid solution

Ferroelectric single crystals of a new lead-reduced Bi(Zn1/2Ti1/2)O3-PbZrO3-PbTiO3 (BZT-PZ-PT) ternary solid solution system have been grown for the first time by three different methods, namely high temperature solution growth (HTSG, or flux method), top-cooled solution growth (TCSG), and top-seeded solution growth (TSSG). The chemical and thermodynamic parameters, including the flux concentration, the soaking temperature and the cooling rate, have been optimized, leading to the growth of good quality BZT-PZ-PT crystals of pseudo-cubic morphology. A large size crystal of the dimensions of 2 × 2 × 0.5 cm3 has been obtained by the TSSG technique. The crystal structure is analyzed by means of X-ray powder diffraction. The highest ferroelectric Curie temperature TC of the grown crystals is found to be 320 °C by means of dielectric measurements. A remnant polarization of 32 μC/cm2 is displayed with a coercive field of 15.4 kV/cm. The high TC and large coercive field of the BZT-PZ-PT single crystal make this m...

Complex morphotropic domain structure and ferroelectric properties in high-TC single crystals of a ternary perovskite solid solution

Ferroelectric and piezoelectric materials with a high Curie temperature (TC) have attracted increasing interest due to their requirement in applications under extreme conditions. In this work, novel high-TC ferroelectric single crystals of (0.95 − x)BiScO3–0.05Pb(Cd1/3Nb2/3)O3–xPbTiO3 (BS–PCN–xPT) ternary solid solution with various compositions have been successfully grown. With increasing PT concentration, a composition-induced structural crossover from a rhombohedral phase, through a morphotropic phase boundary (MPB), to a tetragonal phase, is observed. A monoclinic phase (space group Pm) is found at the MPB region. The temperature dependences of the dielectric permittivity reveal high Curie-temperatures of 363–452 °C (at 1 MHz). The macroscopic and mesoscopic ferroelastic/ferroelectric domain structures systemically characterized by polarized light microscopy (PLM) and piezoresponse force microscopy (PFM) reveal the existence of monoclinic domains in the crystals with the MPB composition. In the monoclinic crystals, the remnant polarization (33.2 μC cm−2) is weaker than that in the rhombohedral phase. All compositions studied show a high coercive field (around EC = 40 kV cm−1). The presence of a high TC and a stable poled state signifies that the BS–PCN–xPT single crystals are promising candidates for applications such as electromechanical transducers that can be operated in a wide range of conditions.

Achieving Higher Strength and Sensitivity toward UV Light in Multifunctional Composites by Controlling the Thickness of Nanolayer on the Surface of Glass Fiber

The interphase between fiber and matrix plays an essential role in the performance of composites. Therefore, the ability to design or modify the interphase is a key technology needed to manufacture stronger and smarter composite. Recently, depositing nanomaterials onto the surface of the fiber has become a promising approach to optimize the interphase and composites. But, the modified composites have not reached the highest strength yet, because the determining parameters, such as thickness of the nanolayer, are hardly controlled by the mentioned methods in reported works. Here, we deposit conformal ZnO nanolayer with various thicknesses onto the surfaces of glass fibers via the atomic layer deposition (ALD) method and a tremendous enhancement of interfacial shear strength of composites is achieved. Importantly, a critical thickness of ZnO nanolayer is obtained for the first time, giving rise to a maximal relative enhancement in the interfacial strength, which is more than 200% of the control fiber. In addition, the single modified fiber exhibits a potential application as a flexible, transparent, in situ UV detector in composites. And, we find the UV-sensitivity also shows a strong correlation with the thickness of ZnO. To reveal the dependence of UV-sensitivity on thickness, a depletion thickness is estimated by a proposed model which is an essential guide to design the detectors with higher sensitivity. Consequently, such precise tailoring of the interphase offers an advanced way to improve and to flexibly control various macroscopic properties of multifunctional composites of the next generation.

Structure and Dielectric Properties of a New Solid Solution (1−x)PbTiO3−xDyFeO3

A solid solution system of novel ferroelectric (1−x)PbTiO3-xDyFeO3 ceramics with 0 ≤ x ≤ 0.50 has been synthesized using the solid state reaction method. The X-ray diffraction data at room temperature indicate a composition-induced structural transition from the tetragonal P4mm phase for 0 ≤ x < 0.25 to the cubic Pm-3m phase for x ≥ 0.25. Both the unit cell volume and the tetragonality gradually decrease with increasing x. The grain size of the ceramics is found by Scanning Electron Microscopy to increase first and then decrease with increasing x. The Curie point moves to low temperatures with increasing DyFeO3 concentration and a composition-induced crossover from a normal ferroelectric phase to a ferroelectric state with diffuse phase transition has been observed. Two Havriliak-Negami relaxation processes and a significant contribution from dc conductance were found at high temperature above the temperature of dielectric maximum, Tm. The room temperature ferroelectric polarization shows a decrease with the increase of x. A partial phase diagram of the solid solution system is constructed based on the dielectric, ferroelectric and structural analyses.