Journal of Advanced Dielectrics

Driven by the minimization of total energy, the multi-domain morphology is preferred in as-grown ferroelectrics to reduce the depolarization and strain energy during the paraelectric to ferroelectric phase transition. However, the complicated multi-domain is not desirable for certain high-performance ferroelectric electro-optic devices. In this work, we achieve a reproducible and stable large-area monodomain in as-grown bulk ferroelectric single crystal ${\mathrm{\text{Sn}}}_2{\mathrm{\text{P}}}_2{\mathrm{\text{S}}}_6$. The monodomain dominates the entire single crystal, which is attributed to the internal charge carriers from the photoexcited disproportionation reaction of Sn ions. The charge carriers effectively screen the depolarization field and therefore decrease the depolarization energy and facilitate the formation of monodomain. This work offers a potential approach for engineering bulk ferroelectrics with a stable monodomain, which is desirable for the high-performance ferroelectric electro-optic devices.

High-quality single crystals of ${\mathrm{\text{Bi}}}_2{\mathrm{\text{WO}}}_6$ are grown using a flux method. With different flux growth recipes, we aim to control the crystallization temperature to be lower and higher than the ferroelectric transition temperature, resulting in mono-domain and multi-domain ${\mathrm{\text{Bi}}}_2{\mathrm{\text{WO}}}_6$ crystals, respectively. Abundant ferroelastic orthorhombic twin domains are observed in the multi-domain crystals under an optical microscope. PFM studies unveil the 90${}^{\circ }$ polarization change across those ferroelastic domain walls, as well as the absence of 180${}^{\circ }$ ferroelectric domains in the as-grown multi-domain crystals, indicating a high energy cost of 180${}^{\circ }$ ferroelectric domains. Moreover, a 45${}^{\circ }$ tilt of the 90${}^{\circ }$ ferroelectric domain walls is discovered, and this tilt creates a new type of charged 90${}^{\circ }$ ferroelectric walls, which have not been observed in other bulk ferroelectrics.

The domain wall structure of ferroelectric/ paraelectric superlattices can be much more complex due to the influence of the superlattice stacking structure, the in-plane strain induced by the substrate and environmental temperature. In this study, we employed a phase field model to investigate the domain wall state of the SrTi${\mathrm{\text{O}}}_3$/BaTi${\mathrm{\text{O}}}_3$ superlattice structure. The domain wall thickness for the SrTi${\mathrm{\text{O}}}_3$/BaTi${\mathrm{\text{O}}}_3$ layer was measured using a hyperbolic function. Based on the simulation results, here, we show a domain wall state diagram to distinguish the hard and soft domain states. The polarization profiles across hard/ soft domain walls were illustrated and analyzed. Our simulation results offer a useful concept for the control of the domain wall state in the ferroelectric superlattice.

We report a straightforward tool to investigate insulator-metal transition in RCo${\mathrm{\text{O}}}_3$ (R = Pr, and Nd) nanoparticles prepared by a sol–gel technique. Thermogravimetric analysis (TGA) of the as-prepared gel is performed to get the lowest possible calcination temperature of RCo${\mathrm{\text{O}}}_3$ nanoparticles. The Rietveld refinement of the powder X-ray diffraction (XRD) patterns for both samples shows that the samples crystallize in the orthorhombic (Pnma) phase at room temperature. The particle size of the sample is determined by scanning electron microscopy. Ac conductivity of the materials is analyzed in the temperature range from 303 K to 673 K and in the frequency range from 42 Hz to 1.1 MHz. The insulator-to-metal transition of PrCo${\mathrm{\text{O}}}_3$ and NdCo${\mathrm{\text{O}}}_3$ is analyzed by ac impedance spectroscopy. DC resistivity measurement is also done to cross check the insulator-metal transition in RCo${\mathrm{\text{O}}}_3$ system.

Mn${\mathrm{\text{O}}}_2$-modified ${\mathrm{\text{Pb}}}_{0.9625}{\mathrm{\text{Sm}}}_{0.025}{({\mathrm{\text{Mg}}}_{1/3}{\mathrm{\text{Nb}}}_{2/3})}_{0.71}{\mathrm{\text{Ti}}}_{0.29}{\mathrm{\text{O}}}_3$ ceramics were prepared via a solid-state reaction approach. Results of detailed characterizations revealed that the addition of Mn${\mathrm{\text{O}}}_2$ has influence on the grain size, and all samples exhibit a pure perovskite structure. As the content of manganese increases, the volume of tetragonal phase increases. The ceramics with 1.5 mol.% Mn${\mathrm{\text{O}}}_2$ show a high electro-strain of 0.151% at 2 kV/mm. Therefore, this study provides a new insight into the role of Mn${\mathrm{\text{O}}}_2$ addition in tailoring the electrical properties of the Sm-PMN-PT ceramics by acceptor doping.

Enhancing the availability and reliability of dielectric ceramic energy storage devices is of great importance. In this work, (1-$x$)${\mathrm{\text{Na}}}_{0.5}{\mathrm{\text{Bi}}}_{0.5}{\mathrm{\text{TiO}}}_3$–$x$Bi(${\mathrm{\text{Mg}}}_{0.5}{\mathrm{\text{Hf}}}_{0.5}$)${\mathrm{\text{O}}}_3$ (NBT–$x$BMH) lead-free ceramics were created utilizing a solid-state reaction technique. All NBT–$x$BMH ceramics have a single perovskite structure. With increasing BMH doping, the grain size shrinks drastically, which greatly enhances the breakdown electric field (310 kV/cm at $x$ = 0.25). Additionally, the relaxation behaviors of NBT–$x$BMH ceramics with high BMH content are more remarkable. Among all designed components, the NBT–0.25BMH ceramic exhibits the best energy storage performance with a high $W_{\mathrm{\text{rec}}}$ of 4.63 J/${\mathrm{\text{cm}}}^3$ and an $\eta$ of 75.1% at 310 kV/cm. The NBT–0.25BMH ceramic has exceptional resistance to fluctuations in both frequency (5–500 Hz) and temperature (30–100${}^{\circ }$C). Charge–discharge test shows that the NBT–0.25BMH ceramic has a quick discharge rate ($t_{0.9}<$ 110 ns). With these properties, the NBT–0.25BMH ceramic may have applications in microdevices as well as in ultra-high power electronic systems.

Lead-free (${\text{K}}_{0.5}$${\text{Na}}_{0.5}$)NbO₃ (KNN) and ${\text{Li}}_{0.06}$(${\text{K}}_{0.5}$${\text{Na}}_{0.5}$)${}_{0.94}$NbO₃ (LKNN) thin films were fabricated by a sol-gel method. The effects of Li substitution on crystal structure, microstructure and electrical properties of KNN film were systematically studied. Li doping can enhance the ferroelectric and piezoelectric properties of KNN film. Compared with pure KNN film, the LKNN film possesses larger remanent polarization ($P_r$ $\sim$ 9.3 $\mu$C/${\mathrm{\text{cm}}}^2$) and saturated polarization ($P_s$ $\sim$ 41.2 $\mu$C/${\mathrm{\text{cm}}}^2$) and lower leakage current density ($\sim {10}^{-5}$A/${\mathrm{\text{cm}}}^2$ at 200 kV/cm). Meanwhile, a typical butterfly shaped piezoelectric response curve is obtained in the LKNN film with a high piezoelectric coefficient ($d_{33}$ $\sim$ 105 pm/V). Excellent fatigue resistance ($\sim$${10}^9$ switching cycles) and aging resistance ($\sim$ 180 days) demonstrate the long-term working stability of LKNN film. These findings indicate that KNN-based lead-free piezoelectric films have a broad application prospect in microelectromechanical systems (MEMS).

In this report, the processes of texture formation in grain-oriented ferroelectric ceramics based on layer-structured ferroelectric Bi₄Ti₃O₂ (LSBT) prepared by hot forging method are considered. The microstructural and X-ray methods revealed the axial textured formation in ferroelectric ceramic that are used to estimate the orientation factor of ceramics. For the first time, the domain structure changes when poling the anisotropic ferroelectric ceramics are investigated. The anisotropy of electromechanical, piezoelectric and ferroelectric properties of ferroelectric ceramics due to the crystal texture existence in it is studied. The aim of this study is to study the processes of crystalline texture formation in polycrystalline BLSF and to establish the dependence of the electrophysical properties of ceramics on the degree of texturing. Ceramics were textured using the hot stamping (HS) method developed at the Research Institute of Physics. The mechanism of the method is that the workpiece is subjected to uniaxial pressure and free radial deformation occurs due to the plastic flow of the material until the workpiece fills the free volume of the mold, which is created by placing the workpiece in the mold with a gap. The study of the microstructure of ceramics showed that an increase in the firing temperature in the range 950–1050${}^{\circ }$C causes a sharp decrease in porosity and increases the density to 7.95 g/${\mathrm{\text{cm}}}^3$, which is 98% of theoretical. An X-ray analysis was performed and microstructural studies were carried out, which revealed the formation of an axial texture in ceramics. The features of the switching processes of textured ceramics are revealed. The characteristics of the polarization switching of ceramics in the directions parallel and perpendicular ($\perp$) of the pressure axis during hot processing were obtained from the dielectric hysteresis $P$($E$) loops, i.e., axis axial texture. The $\perp$-cut ceramics are characterized by a more complete polarization switching, which is associated with the additional orientation of the (001) crystallographic planes in the textured material, as well as the presence of a threshold switching field. In the temperature range from -196 to + 600${}^{\circ }$C, the anisotropy of the electro physical properties of ceramics due to the presence of a crystalline texture in it was studied. The dielectric constant, electrical conductivity, piezoelectric and elastic coefficients were measured for sections of ceramics of different orientations relative to the axis of the texture. The anisotropy of the dielectric constant and electrical conductivity manifests itself weakly at room temperature and increases sharply when approaching the Curie temperature. In the temperature range +20–400${}^{\circ }$C, the high thermal stability of the piezoelectric module $d_{33}$, measured by the quasistatic method, was established.