Mechanochemical synthesis of NaNbO3, KNbO3 and K0.5Na0.5NbO3

Mechanochemical synthesis of the K0.5Na0.5NbO3 solid solution (KNN) is studied. In order to explore the mechanochemical interactions between the constituents in the Na2CO3 - K2CO3 - Nb2O5 system, NaNbO3 and KNbO3 as the boundary compositions of the KNN solid solution are also studied. It has been shown that NaNbO3 can be prepared by a single-step mechanochemical synthesis, while in the case of K2CO3 and Nb2O5, and Na2CO3, K2CO3 and Nb2O5 mixtures, only amorphisation occurs even after prolonged milling

Dual strain mechanisms in a lead-free morphotropic phase boundary ferroelectric

Electromechanical properties such as d33 and strain are significantly enhanced at morphotropic phase boundaries (MPBs) between two or more different crystal structures. Many actuators, sensors and MEMS devices are therefore systems with MPBs, usually between polar phases in lead (Pb)-based ferroelectric ceramics. In the search for Pb-free alternatives, systems with MPBs between polar and non-polar phases have recently been theorized as having great promise. While such an MPB was identified in rare-earth (RE) modified bismuth ferrite (BFO) thin films, synthesis challenges have prevented its realization in ceramics. Overcoming these, we demonstrate a comparable electromechanical response to Pb-based materials at the polar-to-non-polar MPB in Sm modified BFO. This arises from ‘dual’ strain mechanisms: ferroelectric/ferroelastic switching and a previously unreported electric-field induced transition of an anti-polar intermediate phase. We show that intermediate phases play an important role in the macroscopic strain response, and may have potential to enhance electromechanical properties at polar-to-non-polar MPBs

Локальное переключение поляризации в керамике феррита висмута легированной Sm

Работа выполнена с использованием оборудования УЦКП «Современные нанотехнологии» УрФУ при финансовой поддержке РФФИ (Грант 16-32-60083-mol_a_dk)

Tip-induced domain and phase structure transformation in lead free bismuth ferrite ceramics

The equipment of the Ural Center for Shared Use “Modern nanotechnology” UrFU was used. The research was made possible in part by the financial support of RFBR (Grant 16-32-60083-mol_a_dk)

Quantitative phase separation in multiferroic Bi0.88Sm0.12FeO3 ceramics via piezoresponse force microscopy

BiFeO3 (BFO) is a classical multiferroic material with both ferroelectric and magnetic ordering at room temperature. Doping of this material with rare-earth oxides was found to be an efficient way to enhance the otherwise low piezoelectric response of unmodified BFO ceramics. In this work, we studied two types of bulk Sm-modified BFO ceramics with compositions close to the morphotropic phase boundary (MPB) prepared by different solid-state processing methods. In both samples, coexistence of polar R3c and antipolar P-bam phases was detected by conventional X-ray diffraction (XRD); the non-polar P-nma or P-bnm phase also has potential to be present due to the compositional proximity to the polar-to-non-polar phase boundary. Two approaches to separate the phases based on the piezoresponse force microscopy measurements have been proposed. The obtained fractions of the polar and non-polar/anti-polar phases were close to those determined by quantitative XRD analysis. The results thus reveal a useful method for quantitative determination of the phase composition in multi-phase ceramic systems, including the technologically most important MPB systems. (C) 2015 AIP Publishing LLC

Local study of electric field induced phase transition anti-ferroelectric-ferroelectric in lead-free bismuth ferrite ceramics

The equipment of the Ural Center for Shared Use “Modern nanotechnology” UrFU was used. The research was made possible in part by the Ministry of Education and Science of the Russian Federation (Contract 14.587.21.0022, UID RFMEFI58715X0022)

Functional properties of the charged domain walls and phase boundaries in the BiFeO3 thin films and bulk ceramics

In this contribution, we go deeper in understanding the local properties of the interfaces in BFO thin films and RE-BFO ceramics in order to build a comprehensive behavioral model that captures both local and macroscopic electromechanical properties in the same materials.The equipment of the Ural Center for Shared Use "Modern nanotechnology" UrFU was used

Dielectric Relaxation and Charged Domain Walls in (K,Na)NbO3-Based Ferroelectric Ceramics

The influence of domain walls on the macroscopic properties of ferroelectric materials is a well known phenomenon. Commonly, such “extrinsic” contributions to dielectric permittivity are discussed in terms of domain wall displacements under external electric field. In this work, we report on a possible contribution of charged domain walls to low frequency (10-106 Hz) dielectric permittivity in K1-xNaxNbO3 ferroelectric ceramics. It is shown that the effective dielectric response increases with increasing domain wall density. The effect has been attributed to the Maxwell-Wagner-Sillars relaxation. The obtained results may open up possibilities for domain wall engineering in various ferroelectric materials. © 2017 Author(s).The equipment of the Ural Center for Shared Use "Modern Nanotechnology" UrFU has been used. The research was made possible by the Ministry of Education and Science of Russian Federation (UID RFMEFI58715X0022). The authors acknowledge E. L. Rumyantsev and M. Morozov for useful discussion