4 research outputs found
Stabilization of Polar Nano Regions in Pb-free ferroelectrics
Formation of polar nano regions through solid-solution additions are known to
enhance significantly the functional properties of ferroelectric materials.
Despite considerable progress in characterizing the microscopic behavior of
polar nano regions, understanding their real-space atomic structure and
dynamics of formation remains a considerable challenge. Here, using the method
of dynamic pair distribution function, we provide direct insights into the role
of solid-solution additions towards the stabilization of polar nano regions in
the Pb-free ferroelectric of Ba(Zr,Ti)O3. It is shown that for an optimum level
of substitution of Ti by larger Zr ions, the dynamics of atomic displacements
for ferroelectric polarization are slowed sufficiently, which leads to
increased local correlation among dipoles below THz frequencies. The dynamic
pair distribution function technique demonstrates unique capability to obtain
insights into locally correlated atomic dynamics in disordered materials,
including new Pb-free ferroelectrics, which is necessary to understand and
control their functional properties
Dynamical origins of weakly coupled relaxor behavior in Sn-doped (Ba,Ca)Ti O3-BiSc O3
The peculiar characteristics of relaxors, viz., a frequency-dependent dielectric permittivity peak and good functional properties (dielectric, electromechanical, electrocaloric, etc.), are attributed to nanoscale regions with correlated dipoles, or polar nanoregions (PNRs). However, the exact nature of PNRs and their contribution to relaxor behavior remains debatable. In recent years, solid solutions of BaTiO3-BiMeO3 (where Me is a metal), have emerged as an interesting system with characteristics in between that of relaxors and dipole glasses. Here, we have examined the atomistic origins of weakly coupled relaxor behavior, specifically with regard to formation of PNRs, in Sn-doped (1-x)(Ba,Ca)TiO3-xBiScO3 using macroscopic polarization and neutron dynamic pair distribution function measurements. We show that the short-range atomic correlations observed within the PNRs dynamically fluctuate with frequencies of the order of THz. Furthermore the composition-dependent dielectric and polarization behaviors are critically influenced by the relative stability of the atomic correlations near ∼1 THz, while the instantaneous atomic correlations are largely independent of x. The current results are discussed based on a model of intrinsic local modes distributed in a dielectrically soft matrix
Effect of A-site substitutions on energy storage properties of BaTiO 3 -BiScO 3 weakly coupled relaxor ferroelectrics
Weakly coupled relaxors based on compositions (1-x) BaTiO 3 -xBiMeO 3 , where Me is a metal ion, have attracted attention as potential candidates for high-temperature high-energy density capacitors. However, the necessary Bi content is typically high with x = 0.3-0.4. In order to reduce problems associated with compatibility for base metal electrodes and due to additional problems due to Bi volatility, it is desirable to lower the Bi content in the overall composition for these materials. Here, we have explored a possible way to reduce BiMeO 3 content through additional A-site substitutions viz. Ca and Sn. The relaxor nature and energy storage properties of Sn-modified (Ba,Ca)(Ti)O 3 -BiScO 3 ceramics were determined from their dielectric and ferroelectric behaviors. The material showed attractive properties in terms of a frequency-independent (200 Hz-1 MHz) dielectric response from room temperature to 200°C, extremely low loss and high-energy storage efficiency. The structural phenomena underlying the functional properties of Sn-modified (Ba,Ca)TiO 3 -BiScO 3 are characterized from temperature-dependent X-ray diffraction and pair distribution function analysis. In broader terms, the study illustrates the potential for tailoring relaxor behavior in Pb-free ferroelectrics by combining phenomena, such as quantum fluctuations and lone pair stereochemical effect associated with different solid-solution substitutions