Desheng Fu

AgNbO3: A lead-free material with large polarization and electromechanical response

Polarization measurements reveal that AgNbO3 has an extremely large polarization, which can reach a value of 52μC∕cm2 in polycrystals. Experiments also show that the large internal atom distortion in AgNbO3 is also strongly coupled to the electric field, indicating that high piezoelectric performance can be realized in AgNbO3 system. This finding opens the way to designing a new class of lead-free, high-performance piezoelectric materials based on AgNbO3.

Thickness dependence of stress in lead titanate thin films deposited on Pt-coated Si

Thickness dependence of the soft mode E(1TO) of tetraganol lead titanate thin film, deposited on Pt-coated Si by a chemical solution deposition, was determined with Raman scattering measurements. A downshift of the soft mode was attributed to the residual stress in the thin film, which was estimated in the range of 1.3–2.6 GPa, corresponding to film thickness of 400–50 nm. The variation of the clamped dielectric constants determined by observed mode frequencies was found to agree with the prediction of stress dependence of dielectric constants by Devonshire theory.

High-Pressure Synthesis and Correlation between Structure, Magnetic, and Dielectric Properties in LiNbO3-Type MnMO3 (M = Ti, Sn)

LiNbO(3)-type MnMO(3) (M = Ti, Sn) were synthesized under high pressure and temperature; their structures and magnetic, dielectric, and thermal properties were investigated; and their relationships were discussed. Optical second harmonic generation and synchrotron powder X-ray diffraction measurements revealed that both of the compounds possess a polar LiNbO(3)-type structure at room temperature. Weak ferromagnetism due to canted antiferromagnetic interaction was observed at 25 and 50 K for MnTiO(3) and MnSnO(3), respectively. Anomalies in the dielectric permittivity were observed at the weak ferromagnetic transition temperature for both the compounds, indicating the correlation between magnetic and dielectric properties. These results indicate that LiNbO(3)-type compounds with magnetic cations are new candidates for multiferroic materials.

Ferro- and piezoelectric properties of polar-axis-oriented CaBi4Ti4O15 films

Polar-axis-oriented CaBi4Ti4O15 (CBTi144) films were fabricated on Pt foils using a complex metal alkoxide solution. The 500-nm-thick film showed the columnar structure and consisted of well-developed grains. The a/b-axis orientation of the ferroelectric films is considered to be associated with the preferred orientation of Pt foil. The film showed good ferro- and piezoelectric properties. The Pr and Ec were 25 μC/cm2 and 306 kV/cm, respectively, at an applied voltage of 115 V. The d33 was characterized as 30 pm/V by piezoresponse force microscopy. The values were twice as large as those of the CBTi144 thin film with random orientation. The polar-axis-oriented CBTi144 films would open up possibilities for devices as Pb-free piezoelectric materials.

High-piezoelectric behavior of c-axis-oriented lead zirconate titanate thin films with composition near the morphotropic phase boundary

The piezoelectric responses of c-axis-oriented Pb(Zr0.53Ti0.47)O3 (PZT) thin films have been studied by measuring the stress-induced charge with an accurate charge integrator. These measurements reveal that the c-axis-oriented PZT films have high values of d33, which are several times those of ceramic materials. The intrinsic d33 values of poled films are about 680 and 800 pC/N for the c-axis-oriented films on Si and MgO single-crystal substrates, respectively. It shows that the thin-film deposition technique opens an approach for exploring the potential superior properties of PZT near the morphotropic phase boundary.

Crystal growth and piezoelectricity of BaTiO3–CaTiO3 solid solution

We report the crystal growth and piezoelectric properties of (1−x)BaTiO3–xCaTiO3. It is found that the perovskite structure is facilitated by incorporating small Ca into Ba site and single crystals for a wide composition range of 0.02⩽x⩽0.34 can be grown by the floating zone technique with a high rate of 20mm∕h. High values of piezoelectric coefficient (d33=180–310pC∕N) have been demonstrated for the single crystals as well as the biphasic polycrystals with composition close to the solid solution limit. These findings may stimulate further interests in the developments of lead-free piezoelectrics or optical devices.

Grain Size Effect on Dielectric and Piezoelectric Properties of Alkoxy-Derived BaTiO3-Based Thin Films

Lead- and bismuth-free Ba(Ti1-xZrx)O3 (BTZ) thin films were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates by the chemical solution deposition (CSD) process. The BaTiO3 and BTZ005 thin films fabricated by the conventional process were observed to have a remarkable difference in grain size along the depth of the thin film. The microstructure of the BaTiO3 and BTZ005 thin films was improved by additional sintering process, and their grain sizes were increased to about 60 and 40 nm, respectively, by additional sintering at 800°C for 1 h. The dielectric constant er and piezoelectric constant d33 of the BaTiO3 thin film consisting of large grains by the additional sintering at 800°C for 1 h were found to be about 375 and 14.5 pm/V. But, er and d33 of the BTZ005 thin film changed negligibly with increasing of the grain size.

Positive and negative magnetodielectric effects in A-site ordered (BiMn3)Mn4O12 perovskite

A-site ordered perovskite (BiMn3)Mn4O12 was synthesized through a high-pressure synthesis route at 5 GPa and found to exhibit two magnetic transitions and to show either a positive or a negative magnetodielectric effect depending on the temperature range/magnetic state.

Invariant lattice strain and polarization in BaTiO3?CaTiO3 ferroelectric alloys

We report the lattice strain and polarization of the BaTiO(3)-CaTiO(3) solid solution. We found that the lattice strain evaluated by the tetragonality of the tetragonal phase at room temperature is nearly independent of the composition within the limit of the solid solution. In association with this variation, the saturation polarization remains nearly unchanged. Such invariant lattice strain associated with the ionic displacement in ferroelectrics is considered to be responsible for the nearly compositional independence of the polarization and the observed ferroelectric Curie temperature. Its relatively stable polarization compared with that of pure BaTiO(3) is very interesting for technological applications, such as in ferroelectric memory.

Platinum-assisted phase transition in bismuth-based layer-structured ferroelectric CaBi4Ti4O15 thin films

The phase transition of nonferroelectric pyrochlore to ferroelectric perovskite in CaBi4Ti4O15 thin films depends on platinum bottom electrodes. Rather than the strain and crystallinity of the bottom electrode, matching of the atomic arrangement to the Ca–Bi–Ti–O thin films is predominant. CaBi4Ti4O15 thin films crystallized on (200)-oriented platinum at 650 °C showed c-axis orientation. In contrast, thin films crystallized on highly crystalline (111)-oriented platinum at the same temperature contained pyrochlore grains which were about several tens of nanometers in diameter and located in the interface region. They showed P–V hysteresis loops. The remanent polarization and coercive electric field depended on platinum top electrode size.