Daniel S. Tinberg

Structural and electrical characterization of xBiScO3–(1−x)BaTiO3 thin films

Using a tolerance factor approach, it was predicted that xBiScO3–(1−x)BaTiO3 will have a morphotropic phase boundary that should enhance both the polarizability and permittivity, relative to the BiScO3 end member, near a composition of x=0.4. To verify this prediction, pulsed laser deposition was used to grow xBiScO3–(1−x)BaTiO3 thin films on (100) SrRuO3∕LaAlO3 and Pt-coated Si substrates. Typical growth conditions were 700°C and 100mTorr O2∕O3. The perovskite structure was found to be stable for compositions of x=0.2–0.6 in epitaxial films, with reduced stability in polycrystalline films. The temperature where the maximum permittivity occurs rises as BiScO3 is added to BaTiO3, and increasingly relaxorlike behavior is observed with increasing BiScO3 content. Room temperature permittivity values ranged from 200 to 400, with loss tangents of ∼0.1 at 10kHz. The experimental morphotropic phase boundary occurs near x=0.4. 0.4BiScO3–0.6BaTiO3 showed a broad permittivity maximum near 800 from 150–275°C. Films w...

Mapping piezoelectric nonlinearity in the Rayleigh regime using band excitation piezoresponse force microscopy

Band excitation piezoresponse force microscopy enables local investigation of the nonlinear piezoelectric behavior of ferroelectric thin films. However, the presence of additional nonlinearity associated with the dynamic resonant response of the tip-surface junction can complicate the study of a material’s nonlinearity. Here, the relative importance of the two nonlinearity sources was examined as a function of the excitation function. It was found that in order to minimize the effects of nonlinear tip-surface interactions but achieve good signal to noise level, an optimal excitation function must be used.

Composition dependence of local piezoelectric nonlinearity in (0.3)Pb(Ni0.33Nb0.67)O3-(0.7)Pb(ZrxTi1−x)O3 films

The composition dependence of dielectric and piezoelectric nonlinearities were characterized in epitaxially grown (0.3)Pb(Ni0.33Nb0.67)O3-(0.7)Pb(ZrxTi1−x)O3 thin films deposited on SrTiO3. Tetragonal, morphotropic phase boundary (MPB) and rhombohedral films were prepared by changing the Zr/Ti ratio. The relative dielectric permittivity ɛr and the converse piezoelectric coefficient d33,f were found to follow the Rayleigh law. The local piezoelectric nonlinearity map showed the formation of micron-sized clusters of higher nonlinear activity for the MPB and rhombohedral compositions. The ratios of the irreversible to the reversible Rayleigh constants αɛ/ɛinit and the spatially averaged αd/d33,init ratio were larger for the rhombohedral and MPB compositions compared to the tetragonal composition. The larger dielectric and piezoelectric nonlinearities observed for the rhombohedral sample are interpreted in terms of a higher domain wall mobility due to a smaller ferroelectric distortion and superior crystal qu...

Coherently strained epitaxial Pb(Zr1−xTix)O3 thin films

Coherently strained Pb(Zr1−xTix)O3, 0.2 ≤ x ≤ 0.35, thin films were grown by pulsed laser deposition on (001) and (111) oriented SrTiO3 substrates. A buffer layer of Pb(Zr0.6Ti0.4)O3 was used to improve the lattice matching and induce compressive strain in Zr-rich compositions. The (001)pc (pc = pseudocubic) films showed an increased ferroelectric transition temperature, TC, compared to bulk ceramics, but the transition from an untilted to a tilted ferroelectric (TTilt) exhibited only a modest increase in temperature. This suggests that it may be possible to enlarge the untilted ferroelectric phase field by compressive strain. Consistent with previous work on relaxed PZT films, coherently strained PZT films do not exhibit an abrupt transition from an untilted to a tilted state; rather, a region of non-zero tilt exists above TTilt. (111)pc films also showed an increased ferroelectric transition temperature with a weak strain dependence on TTilt. The compressive strain in (111)pc films induced a preferred d...

Structural phase transitions in AgTa0.5Nb0.5O3 thin films

Octahedral tilt transitions in epitaxial AgTa0.5Nb0.5O3 (ATN) films grown on (001)p (where p=pseudocubic) oriented SrRuO3/LaAlO3 and LaAlO3 substrates were characterized by electron diffraction and high resolution x-ray diffraction. It was found that the ATN films exhibited octahedral rotations characteristic of the Pbcm space group, similar to those seen in bulk materials; however, the temperature of the M3↔M2 phase transition has been suppressed by ∼250 K due to the fact that the correlation length for rotations about cp was significantly reduced. The average off-center B-cation displacements, which signify the degree of long-range order for these local cation positions, were negligibly small compared to bulk materials, as inferred from the near-zero intensity of the 1/4(00l)p-type reflections. On cooling, pronounced ordering of B-cation displacements occurred at ≈60 K which is significantly lower compared to bulk (≈310 K). The onset of this ordering coincides with a broad maximum in relative permittivi...

Octahedral tilt transitions in relaxed epitaxial Pb(Zr1−xTix)O3 films

Relaxed epitaxial {100}pc and {111}pc oriented films (350 nm) of Pb(Zr1−xTix)O3 (0.2 ≤ x ≤ 0.4) on SrRuO3/SrTiO3 substrates were grown by pulsed laser deposition and studied using high resolution synchrotron X-ray diffraction and transmission electron microscopy. The dielectric behavior and ferroelectric phase transition temperatures of the films were consistent with bulk PZT. However, weak 1/2{311}pc reflections in x-ray diffraction profiles were recorded above bulk TTilt (as indicated in the Jaffe, Cooke, and Jaffe phase diagram, where pc denotes pseudocubic indices). Moreover, anomalies in the dielectric and ferroelectric response were detected above TTilt which are explained by coupling of short coherence or weakly tilted regions to the ferroelectric polarization.

Phase transitions and octahedral rotations in epitaxial Ag(TaxNb1-x)O3 thin films under tensile strain

Epitaxial Ag(Ta0.5Nb0.5)O3 (ATN) films under tensile strain were deposited on (Ba0.4Sr0.6)TiO3/LaAlO3 (001)p and KTaO3 (001) substrates. These films exhibited a domain structure with the c-axis aligned primarily along the in-plane direction in contrast with the poly-domain nature of bulk ATN ceramics or relaxed films. While the generic phase transition sequence of the tensile films was qualitatively similar to bulk, the tetragonal and orthorhombic phase field regions expanded by ∼270 °C in ATN/(Ba0.4Sr0.6)TiO3/LaAlO3. Furthermore, the films were found to be in the M3 (complex octahedral tilting with disordered Nb/Ta displacements) phase at room temperature with either significantly reduced tilt angles or a suppression of the long range order of the complex tilt as compared to bulk materials. It was observed that the octahedral tilt domains were oriented with the complex tilt axes lying in the plane of the film due to the tensile strain. This work demonstrates that tensile strain can be used to strain-engi...