arXiv subjects

Michael Knapp

Publications and source records attributed to Michael Knapp.

3 recordsLinked to original sources

arXiv2015

A comprehensive study of the phase diagram of K0.5Na0.5NbO3-Bi0.5Na0.5TiO3 system

The phase diagram of lead-free piezoelectric (1-x)K0.5Na0.5NbO3-xBi0.5Na0.5TiO3 system has been studied by high-resolution synchrotron powder diffraction, neutron powder diffraction and selected area electron diffraction (SAED). The two lead-free piezoelectric compounds, K0.5Na0.5NbO3 and Bi0.5Na0.5TiO3 tend to form an infinite solid solution. The oxygen octahedral tilt system has been mapped as a function of composition and temperature. The results indicate that K0.5Na0.5NbO3-Bi0.5Na0.5TiO3 does not display a morphotropic phase boundary like lead zirconate titanate, and that the most significant structural change as a function of composition occurs near x=0.14 and x=0.87 due to ionic disorder at A and B sites in the perovskite ABO3 structure at room temperature.

cond-mat.mtrl-sci↗

arXiv2015

Structure and dielectric dispersion in cubic-like 0.5K0.5Na0.5NbO3- 0.5Na0.5Bi0.5TiO3 ceramic

The nature of the cubic-like state in the lead-free piezoelectric ceramics 0.5K0.5Na0.5NbO3-0.5Na0.5Bi0.5TiO3 (KNN-50BNT) has been examined in detail by synchrotron x-ray diffraction (SD), selected area electron diffraction (SAED), neutron diffraction (ND), and temperature dependent dielectric characterization. The SD pattern of KNN-50BNT presents a pure perovskite structure with pseudocubic symmetry. However, superlattice reflections were observed by SAED and completely indexed by tetragonal symmetry with P4bm space group in ND pattern. The relaxor behavior of KNN-50BNT is compared with Pb-based and Ba-based relaxors and discussed in the framework of the Vogel-Fulcher law and the new glass model. The KNN-50BNT ceramic exhibits the strongest dielectric dispersion among them.

cond-mat.mtrl-sci↗

arXiv2015

Structural Contribution to the Ferroelectric Fatigue in Lead Zirconate Titanate (PZT) Ceramics

Many ferroelectric devices are based on doped lead zirconate titanate (PZT) ceramics with compositions near the morphotropic phase boundary (MPB), at which the relevant material's properties approach their maximum. Based on a synchrotron x-ray diffraction study of MPB PZT, bulk fatigue is unambiguously found to arise from a less effective field induced tetragonal-to-monoclinic transformation, at which the degradation of the polarization flipping is detected by a less intense and more diffuse anomaly in the atomic displacement parameter of lead. The time dependence of the ferroelectric response on a structural level down to 250 $\mu$s confirms this interpretation in the time scale of the piezolectric strain response.

cond-mat.mtrl-sci↗