Manuel Hinterstein

Design of zeolite by inverse sigma transformation

Although the search for new zeolites has traditionally been based on trial and error, more rational methods are now available. The theoretical concept of inverse σ transformation of a zeolite framework to generate a new structure by removal of a layer of framework atoms and contraction has for the first time been achieved experimentally. The reactivity of framework germanium atoms in strong mineral acid was exploited to selectively remove germanium-containing four-ring units from an UTL type germanosilicate zeolite. Annealing of the leached framework through calcination led to the new all-silica COK-14 zeolite with intersecting 12- and 10-membered ring channel systems. An intermediate stage of this inverse σ transformation with dislodged germanate four-rings still residing in the pores could be demonstrated. Inverse σ transformation involving elimination of germanium-containing structural units opens perspectives for the synthesis of many more zeolites.

High-temperature poling of ferroelectrics

The poling behavior of a lead-zirconate-titanate piezoelectric ceramic is investigated by measurements of the ferroelectric hysteresis, the longitudinal piezoelectric coefficient, and field-cooling poling experiments. At high temperatures, the decrease in the coercive field facilitates poling at lower electric fields, resulting in higher values of the longitudinal piezoelectric coefficient. However, there exists a threshold field of about 150 V/mm, below which fully poled samples cannot be obtained even when field cooling from temperatures above the transition. Further, a temperature regime below the Curie temperature is observed, where a polarization under field can be measured, but a remanent polarization is not stable. The results are discussed with respect to the phase transition behavior.

Synchrotron Diffraction Study of Lithium Extraction from LiMn0.6Fe0.4PO4

Electrochemical lithium extraction from LiMn0.6Fe0.4PO4 was revealed to proceed through two two-phase regions in contrast to the mechanism earlier reported. All phases appearing during charging of the cell have the same olivine-like structure with different cell parameters.

The phase diagram of K0.5Na0.5NbO3–Bi1/2Na1/2TiO3

The phase diagram of the lead-free piezoelectric (1 − x)K0.5Na0.5NbO3–xBi1/2Na1/2TiO3 system has been studied by high-resolution synchrotron powder diffraction, neutron powder diffraction and selected area electron diffraction. The two lead-free piezoelectric materials K0.5Na0.5NbO3 and Bi1/2Na1/2TiO3 form an infinite substitution solid solution. The orthorhombic (O), monoclinic (M), tetragonal (T) and rhombohedral (R) phases and the phase coexistence of M (Pm) + T (P4mm) for 0.02 < x ≤ 0.14, T (P4bm) + pseudocubic (Pm{\overline 3}m) for 0.14 < x ≤ 0.87 and T (P4bm) + R (R3c) for 0.87 < x ≤ 0.96 have been investigated at room temperature, with a subtle change in the structure observed. The oxygen octahedral tilt system has been mapped as a function of composition and temperature. The results indicate that K0.5Na0.5NbO3–Bi1/2Na1/2TiO3 does not display a morphotropic phase boundary like lead zirconate titanate, and that the most significant structural changes as a function of composition occur near x = 0.14 and x = 0.87 as a result of ionic disorder at the A and B sites in the perovskite ABO3 structure at room temperature.

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 materials 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 μs confirms this interpretation in the time scale of the piezolectric strain response.

In situ neutron diffraction study of electric field induced structural transitions in lanthanum doped lead zirconate titanate

Abstract The structural reaction of La-doped PbZr1–xTixO3 (PLZT) with x = 0.44, 0.46 and 0.475 to an electric field was investigated by in situ neutron diffraction. The induced structural changes and the anisotropic displacement parameters were analysed. While the composition with a high Ti content shows a trend to tetragonal characteristics, PLZT with a low Ti content exhibits a rhombohedral response to the applied electric field. The intermediate composition with x = 0.46 appears rhombohedral in the unpoled state. Under the influence of an applied electric field, however, the response is similar to tetragonal PLZT (x = 0.475). With the investigated compositions the field induced processes are characterised. In the tetragonal composition the field dependent variation of the tetragonal lattice distortion is most pronounced. In rhombohedral PLZT (x = 0.44) the pseudorhombohedral lattice distortion exhibits the most significant changes. In the intermediate composition primarily atomic displacements are involved. Hence, a systematic change of the response to an applied electric field is observed while crossing the morphotropic phase boundary.

Temperature-dependent synchrotron powder diffraction phase studies of (K0.37Na0.52Li0.03)(Nb0.87Ta0.1Sb0.03)O3 ferroelectric ceramics

Abstract Temperature-dependent synchrotron powder diffraction measurements have been performed on lead-free ferroelectric (K0.37Na0.52Li0.03)(Nb0.87Ta0.1Sb0.03)O3 ceäramics. The measurement was performed from 20 °C to 400 °C with 20 °C steps. The diffraction patterns showed the existence of two phases from 20 °C to 180 °C while the ferroelectric to paraelectric phase transition occurred between 340 °C and 360 °C. Rietveld refinement using the Fullprof software was employed and the two-phase region was refined using a combination of the orthorhombic phase with space group Amm2 (38) and the tetragonal phase with space group P4mm (99) from 20 °C to 180 °C. The tetragonal phase was used for the refinement up to 340 °C while the cubic phase was refined with space group Pm-3m (221). Good refinement structure parameters were obtained for all temperatures with the average G.O.F being approximately 4.0. Information about the cell parameters and weight fraction of the phases were obtained as a function of temperature.

Piezoelectricity and rotostriction through polar and non-polar coupled instabilities in bismuth-based piezoceramics

Coupling of order parameters provides a means to tune functionality in advanced materials including multiferroics, superconductors, and ionic conductors. We demonstrate that the response of a frustrated ferroelectric state leads to coupling between order parameters under electric field depending on grain orientation. The strain of grains oriented along a specific crystallographic direction, 〈h00〉, is caused by converse piezoelectricity originating from a ferrodistortive tetragonal phase. For 〈hhh〉 oriented grains, the strain results from converse piezoelectricity and rotostriction, as indicated by an antiferrodistortive instability that promotes octahedral tilting in a rhombohedral phase. Both strain mechanisms combined lead to a colossal local strain of (2.4 ± 0.1) % and indicate coupling between oxygen octahedral tilting and polarization, here termed “rotopolarization”. These findings were confirmed with electromechanical experiments, in situ neutron diffraction, and in situ transmission electron microscopy in 0.75Bi1/2Na1/2TiO3-0.25SrTiO3. This work demonstrates that polar and non-polar instabilities can cooperate to provide colossal functional responses.

Structure and dielectric dispersion in cubic-like 0.5K0.5Na0.5NbO3-0.5Na1/2Bi1/2TiO3 ceramic

The nature of the cubic-like state in the lead-free piezoelectric ceramics 0.5K0.5Na0.5NbO3-0.5Na1/2Bi1/2TiO3 (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.

Cyclic electric field response of morphotropic Bi1/2Na1/2TiO3-BaTiO3 piezoceramics

In this study, the evolution of field induced mechanisms in lead-free piezoelectric ceramics (1−x)Bi1/2 Na 1/2TiO3-xBaTiO3 with x = 0.06 and 0.07 was investigated by transmission electron microscopy, neutron, and X-ray diffraction. Preliminary investigations revealed a strong degradation of macroscopic electromechanical properties within the first 100 bipolar electric cycles. Therefore, this structural investigation focuses on a comparative diffraction study of freshly prepared, poled, and fatigued specimens. Transmission electron microscopy and neutron diffraction of the initial specimens reveal the coexistence of a rhombohedral and a tetragonal phase with space group R3c and P4bm, respectively. In situ electric field X-ray diffraction reveals a pronounced field induced phase transition from a pseudocubic state to a phase composition of significantly distorted phases upon poling with an external electric field of 4 kV/mm. Although the structures of the two compositions are pseudocubic and almost indistinguishable in the unpoled virgin state, the electric field response shows significant differences depending on composition. For both compositions, the application of an electric field results in a field induced phase transition in the direction of the minority phase. Electric cycling has an opposite effect on the phase composition and results in a decreased phase fraction of the minority phase in the fatigued remanent state at 0 kV/mm.