Domain matching epitaxy stabilized metastable, tetragonal BiFeO3 on symmetry-mismatched c-plane ZnO

We report the stabilization of metastable tetragonal BiFeO3 epilayer on ZnO(0001) surface. X-ray reciprocal space map characterizations show that the BiFeO3 film is of true tetragonal symmetry, but not the commonly observed monoclinic structure. The critical thickness of the tetragonal BiFeO3 is higher than 140 nm, much larger than that reported previously. Despite the considerable lattice mismatch and symmetry mismatch, tetragonal BiFeO3 can be formed on ZnO(0001) though domain matching epitaxy which is featured by anisotropic growth. We show that by taking into account the elastic energy during the initial semi-coherent growth, the tetragonal phase is lower than the thermally stable rhombohedral phase in total energy by 70 meV per formula unit. Moreover, local piezoelectric characterizations reveal a coercive field of 360 kV/cm and a piezoelectric constant of 48 pm/V. The integration of tetragonal BiFeO3 with robust ferroelectricity on the platform of ZnO has potentials for all-oxide electronics applications.

Electrical and structural properties of pure and self-defected Bi1/2Na1/2TiO3 system: A DFT study

The structural and electronic properties of the rhombohedral phase of the A-site-substituted perovskite Sodium bismuth titanate Bi1/2Na1/2TiO3 (BNT) were investigated via the density functional theory (DFT) that implemented in the CASTEP module in the Materials Studio software. I also investigated the impacts of atoms vacancy and oxygen-dopants on dielectric, electrical conductivity, and ferroelectric properties. The author expected that the defected on lead-free ferroelectric materials could extend the functional materials for innovative electronic applications.

Magnetic Behaviour of Perovskite Compositions Derived from BiFeO3

The phase content and sequence, the crystal structure, and the magnetic properties of perovskite solid solutions of the (1−y)BiFeO3–yBiZn0.5Ti0.5O3 series (0.05 ≤ y ≤ 0.90) synthesized under high pressure have been studied. Two perovskite phases, namely the rhombohedral R3c and the tetragonal P4mm, which correspond to the structural types of the end members, BiFeO3 and BiZn0.5Ti0.5O3, respectively, were revealed in the as-synthesized samples. The rhombohedral and the tetragonal phases were found to coexist in the compositional range of 0.30 ≤ y ≤ 0.90. Magnetic properties of the BiFe1−y[Zn0.5Ti0.5]yO3 ceramics with y < 0.30 were measured as a function of temperature. The obtained compositional variations of the normalized unit-cell volume and the Néel temperature of the BiFe1−y[Zn0.5Ti0.5]yO3 perovskites in the range of their rhombohedral phase were compared with the respective dependences for the BiFe1−yB3+yO3 perovskites (where B3+ = Ga, Co, Mn, Cr, and Sc). The role of the high-pressure synthesis in the formation of the antiferromagnetic states different from the modulated cycloidal one characteristic of the parent BiFeO3 is discussed.

Phase Transformations and Subsurface Changes in Three Dental Zirconia Grades after Sandblasting with Various Al2O3 Particle Sizes

Although sandblasting is mainly used to improve bonding between dental zirconia and resin cement, the details on the in-depth damages are limited. The aim of this study was to evaluate phase transformations and subsurface changes after sandblasting in three different dental zirconia (3, 4, and 5 mol% yttria-stabilized zirconia; 3Y-TZP, 4Y-PSZ, and 5Y-PSZ). Zirconia specimens (14.0 × 14.0 × 1.0 mm3) were sandblasted using different alumina particle sizes (25, 50, 90, 110, and 125 µm) under 0.2 MPa for 10 s/cm2. Phase transformations and residual stresses were investigated using X-ray diffraction and the Williamson-Hall method. Subsurface damages were evaluated with cross-sections by a focused ion beam. Stress field during sandblasting was simulated by the finite element method. The subsurface changes after sandblasting were the emergence of a rhombohedral phase, micro/macro cracks, and compressive/tensile stresses depending on the interactions between blasting particles and zirconia substrates. 3Y-TZP blasted with 110-µm particles induced the deepest transformed layer with the largest compressive stress. The cracks propagated parallel to the surface with larger particles, being located up to 4.5 µm under the surface in 4Y- or 5Y-PSZ subgroups. The recommended sandblasting particles were 110 µm for 3Y-TZP and 50 µm for 4Y-PSZ or 5Y-PSZ for compressive stress-induced phase transformations without significant subsurface damages.

STRUCTURE, MICROSTRUCTURE, AND PIEZOELECTRIC PROPERTIES OF KNLNS-BNKZ LEAD-FREE CERAMICS UNDER THE EFFECT OF DIFFERENT SINTERING TEMPERATURES

Samples of 0.96(K0.48Na0.48Li0.04)(Nb0.95Sb0.05)O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 piezoelectric ceramic were fabricated with conventional ceramic techniques and sintered at different temperatures. The effect of sintering temperature (TS) on the structure, microstructure, and piezoelectric properties of the ceramics was studied in detail. The experimental results showed that with an increase of the TS temperature, the structure of the ceramics transformed from an orthorhombic-tetragonal mixed phase (O-T) at TS £ 1100 °C into a rhombohedral-tetragonal (R-T) mixed phase with a dense microstructure of uniform grain size at TS = 1110 °C. When TS was further increased (TS ³ 1120 °C), the ceramics showed only a rhombohedral phase (R). The ceramics showed the best electrical properties for TS = 1110 °C at which the rhombohedral and tetragonal (R-T) phases coexist. Specifically, the ceramic density reached its highest value (4.22 g/cm3), the electromechanical coupling coefficients kp and kt were 0.46 and 0.50, respectively, and the piezoelectric coefficient d33 was 245 pC/N.

Formation and characterization of an Al-rich metastable phase in the Al–B phase diagram

Vacuum heat treatment of mechanically alloyed powders of boron and aluminium leads to the formation of a metastable Al-rich phase, which can be quenched. Its structure, composition and thermal stability are established. With the chemical formula Al1.28B the rhombohedral phase is unusually rich in Al. The parameters of the unit cell determined from X-ray powder diffraction are a = 18.3464 (19), c = 8.9241 (9) Å, V = 2601.3 (6) Å3, space group R 3. It is stable on heating to 630°C. It is suggested that this phase is an important intermediate step in the formation of AlB2 and, eventually, of other borides; its nucleation and thermal stability are explained by high elastic energy hindering the formation of equilibrium phases at low temperatures.

Optimizing K0.5Na0.5NbO3 Single Crystal by Engineering Piezoelectric Anisotropy

K0.5Na0.5NbO3 is considered as one of the most promising lead-free piezoelectric ceramics in the field of wearable electronics because of its excellent piezoelectric properties and environmental friendliness. In this work, the temperature-dependent longitudinal piezoelectric coefficient d33* was investigated in K0.5Na0.5NbO3 single crystals via the Landau–Ginzburg–Devonshire theory. Results show that the piezoelectric anisotropy varies with the temperature and the maximum of d33max* deviates from the polar direction of the ferroelectric phase. In the tetragonal phase, d33maxt* parallels with cubic polarization direction near the tetragonal-cubic transition region, and then gradually switches toward the nonpolar direction with decreasing temperatures. The maximum of d33o* in the orthorhombic phase reveals a distinct varying trend in different crystal planes. As for the rhombohedral phase, slight fluctuation of the maximum of d33r* was observed and delivered a more stable temperature-dependent maximum d33maxr* and its corresponding angle θmax in comparison with tetragonal and orthorhombic phases. This work not only sheds some light on the temperature-dependent phase transitions, but also paves the way for the optimization of piezoelectric properties in piezoelectric materials and devices.