Papers by Keyword: Ba(Ti_1-xZr_x)O₃

Abstract: The relaxor state has been found in the mixed ferroelectric system Ba (Ti_1-xZr_x)O₃ around x = 0.35. To understand the nature of the relaxor state, the crystallographic features of the paraelectric (PC), ferroelectric, and relaxor states for 0.15 ≤ x ≤ 0.40 have been investigated mainly by transmission electron microscopy. It was found that a microstructure of the ferroelectric state for 0.15 ≤ x ≤ 0.28 consisted of banded structures with boundaries parallel to the {110}_PC and {100}_PC planes. Based on the Sapriel theory concerning ferroelastic transitions, it was understood that the banded structures were consistent with domain structures in the ferroelectric rhombohedral (FR) state having a polarization vector parallel to one of the <111>_PC directions. With the help of the failure of Friedel’s law in diffraction, furthermore, polar regions having <001>_PC and <110>_PC components of a <111>_PC polarization vector were also found to be separately observed in the PC and relaxor states as well as the FR state. Then, in-situ observation for 0.29 ≤ x ≤ 0.40 made in this study indicated that the PC and relaxor states consisted of polar nanometer-sized regions having these two components. Based on this, the relaxor state in BTZ can be identified as an assembly of polar nanometer-sized regions, which were produced by the suppression of the (PC→FR) ferroelectric transition on cooling.

Abstract: The mixed-oxide system Ba (Ti_1-xZr_x)O₃ (BTZ) with the simple perovskite structure was reported to exhibit the remarkable dielectric response around x = 0.08. In order to understand the origin of the response, we have investigated the crystallographic features of ferroelectric states in BTZ with 0 ≤ x ≤ 0.15 mainly by transmission electron microscopy. According to the constructed phase diagram of BTZ, when the Zr content increases from x = 0 around 300 K, the ferroelectric tetragonal state in BaTiO₃ is changed into the ferroelectric orthorhombic state around x = 0.03, and then into the ferroelectric monoclinic state around x = 0.06. That is, the monoclinic state with a polarization vector in the {110}_PC planes is present in BTZ with 0.07 ≤ x ≤ 0.15, where the subscript PC denotes the paraelectric cubic state. The notable feature of the monoclinic state is that it exhibits the herringbone-type domain structure consisting of nanometer-sized ferroelectric domains. It is thus understood that the remarkable dielectric response in BTZ should be associated with the presence of nanometer-sized domains with the monoclinic symmetry.

Abstract: Lead-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 microstructure of the BTZ (x = 0.00 to 0.20) thin films was improved by additional sintering process, and their crystallite sizes were increased in each composition. The dielectric constant er and piezoelectric constant d33 of the BTZ thin films depended on the crystallite size. We give a guide for further investigation to improve the characteristics of BTZ thin films.