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Register a new userGround state of (Pb0.94Sr0.06)(Zr0.530Ti0.470)O3 in the morphotropic phase boundary region: Evidence for a monoclinic Cc space group
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Added by
Ravindra Singh Solanki
Publication date
2014
fields
Physics
and research's language is
English
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The antiferrodistortive (AFD) phase transition for a pseudotetragonal composition of Pb(Zr0.530Ti0.470)O3 (PZT) doped with 6% Sr has been investigated using sound velocity (4 to 320K), high resolution synchrotron X-ray powder diffraction (100 to 800K) and high resolution as well as high flux neutron powder diffraction measurements (4K) to settle the existing controversies about the true ground state of PZT in the morphotropic phase boundary (MPB) region. The multiplet character of the neutron diffraction profiles of (3/2 1/2 1/2)pc (pseudocubic or pc indices) and (3/2 3/2 1/2)pc superlattice peaks, appearing below the AFD transition temperature, rules out the rhombohedral R3c space group. The true ground state is confirmed to be monoclinic in the Cc space group in agreement with the predictions of the first principles calculations and earlier findings for pure PZT in the MPB region. 6% Sr2+ substitution and the use of high wavelength ({lambda}=2.44{AA}) neutrons have played key role in settling the existing controversies about the true ground state of PZT in the MPB region.
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In this work, we address the issue of peaking of piezoelectric response at a particular composition in the morphotropic phase boundary (MPB) region of (Pb0.940Sr0.06)(ZrxTi1-x)O3 (PSZT) piezoelectric ceramics. We present results of synchrotron x-ray powder diffraction, dielectric, piezoelectric and sound velocity studies to critically examine the applicability of various models for the peaking of physical properties. It is shown that the models based on the concepts of phase coexistence, polarization rotation due to monoclinic structure, tricritical point and temperature dependent softening of elastic modulus may enhance the piezoelectric response in the MPB region in general but cannot explain its peaking at a specific composition. Our results reveal that the high value of piezoelectric response for the MPB compositions in PSZT at x=0.530 is due to the softening of the elastic modulus as a function of composition. The softening of elastic modulus facilitates the generation of large piezoelectric strain and polarization on approaching the MPB composition of x=0.530. This new finding based on the softening of elastic modulus may pave the way forward for discovering/designing new lead-free environmentally friendly piezoelectric materials and revolutionize the field of piezoelectric ceramics.
Morphotropic phase boundaries (MPBs) show substantial piezoelectric and dielectric responses, which have practical applications. The predicted existence of MPB in HfO2-ZrO2 solid solution thin film has provided a new way to increase the dielectric properties of a silicon-compatible device. Here, we present a new fabrication design by which the density of MPB and consequently the dielectric constant of HfO2-ZrO2 thin film was considerably increased. The density of MPB was controlled by fabrication of a 10-nm [1 nm-Hf0.5Zr0.5O2 (Ferroelectric)/1 nm-ZrO2 (Antiferroelectric)] nanolaminate followed by an appropriate annealing process. The coexistence of orthorhombic and tetragonal structures, which are the origins of ferroelectric (FE) and antiferroelectric (AFE) behaviors, respectively, was structurally confirmed, and a double hysteresis loop that originates from AFE ordering, with some remnant polarization that originates from FE ordering, was observed in P-E curve. A remarkable increase in dielectric constant compared to the conventional HfO2-ZrO2 thin film was achieved by controlling the FE-AFE ratio. The fabrication process was performed at low temperature and the device is compatible with silicon technology, so the new design yields a device that has possible applications in near-future electronics.
We have investigated heteroepitaxial films of Sm-doped BiFeO3 with a Sm-concentration near a morphotropic phase boundary. Our high-resolution synchrotron X-ray diffraction, carried out in a temperature range of 25C to 700C, reveals substantial phase coexistence as one changes temperature to crossover from a low-temperature PbZrO3-like phase to a high-temperature orthorhombic phase. We also examine changes due to strain for films greater or less than the critical thickness for misfit dislocation formation. Particularly, we note that thicker films exhibit a substantial volume collapse associated with the structural transition that is suppressed in strained thin films.
We report here the structure and dielectric studies on a new lead free (1-x)BaTiO3-xBi(Mg1/2Zr1/2)O3 solid solution to explore the morphotropic phase boundary. The powder x-ray diffraction studies on (1-x)BaTiO3-xBi(Mg1/2Zr1/2)O3 solid solution suggests that structure is tetragonal (P4mm) for the composition with x=0.05 and cubic for the composition with x=0.30 and 0.40. Morphotropic phase boundary is observed in the composition range 0.10<x<0.30, where phase coexistence is observed and composition dependence of room temperature permittivity shows a peak. High temperature dielectric measurement for the composition with x=0.20 exhibits diffuse phase transition having peak temperature around ~ 396 K at 10 kHz. The diffuseness parameter ({gamma}) was obtained to be 1.68 for composition with x=0.20.
Two-dimensional polarity is intriguing but remains in the early stage. Here a structural evolution diagram is established for GeS monolayer, which leads a noncollinear ferrielectric $delta$-phase energetically as stable as the ferroelectric $alpha$-phase. Its ferrielectricity is induced by the phonon frustration, i.e., the competition between ferroelectric and antiferroelectric modes, providing more routes to tune its polarity. Besides its prominent properties like large band gap, large polarization, and high Curie temperature, more interestingly, the morphotropic phase boundary between $alpha$- and $delta$-phases is highly possible, which is crucial to obtain giant piezoelectricity for lead-free applications.
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