High temperature stress-induced “double loop-like” phase transitions in Bi-based perovskites

Abstract

Polycrystalline 0.94(Bi1/2Na1/2)TiO3–0.06BaTiO3 samples were tested under uniaxial mechanical compression at various temperatures in the vicinity of the polar tetragonal to nonpolar tetragonal phase boundary. They are shown to display double loop-like stress-strain behavior, marked by a closed ferroelastic hysteresis loop. Thus, it forms a mechanical analog to the polarization-electric field hysteresis behavior of barium titanate above the Curie temperature. As temperature is increased there is an apparent loss of macroscopically observable ferroelasticity, despite the persistence of tetragonality. Macroscopic experimental results are discussed in conjunction with temperature-dependent and stress-dependent high-energy x-ray diffraction data. This reveals a phase transition below the Curie temperature, marked by a discontinuous change in lattice parameters and octahedral tilting during compressive mechanical loading.

Stress-modulated relaxor-to-ferroelectric transition in lead-free(Na1/2Bi1/2Schader1, Wang2, Hinterstein3 et al. 2016Phys. Rev. B885462View full textAdd to dashboardCite

“…found that the coercive stress of NBT-0.06BT at room temperature was approximately −275 MPa, corresponding well to the present experimental data [60]. There is, however, no clear saturation in the room temperature relative permittivity decrease, as would be expected when the relaxor-to-long-range ferroelectric order transition is exhausted.…”

Evolving morphotropic phase boundary in lead-free (Bi1/2Na1/2)TiO3–BaTiO3 piezoceramics

“…As expected, the compositional dependence of the dielectric properties changes significantly after the poling treatment. A sharp maximum in 33 This implies that the structural phase boundary that occurs at BNT-11BT is not responsible for the maximization of the electromechanical properties. Instead, this property enhancement is induced on the rhombohedral-rich side of the electric-field-induced MPB regime, i.e., at BNT-6BT and BNT-7BT.…”

“…To investigate this, we monitored the evolution of piezoelectric coefficient d 33 and permittivity r of two compositions ͑BNT-7BT and BNT-9BT͒ in situ during the poling cycle ͓Figs. 7͑a͒ and 7͑b͔͒.…”

“…30,33 Beam energies of 87.19 keV and 68.02 keV were selected for the in situ electric-field-dependent and stress-dependent experiments, respectively. At these beam energies, a 1 mm thick BNT-BT sample is transparent, and thus diffraction information is collected from the bulk of the material.…”

“…[16][17][18][19][20][21] The ͑1−x͒͑Bi 1/2 Na 1/2 ͒TiO 3 -100xBaTiO 3 ͑BNT-100xBT͒ system has been of great interest since the discovery of an MPB, where a rhombohedral and a tetragonal symmetry coexist, in the system in 1991. 22 The interest has arisen largely because the MPB was reported to separate the rhombohedral BNT and the tetragonal BT as in PZT, accompanied by a significant enhancement in the dielectric permittivity and electromechanical coupling factor k 33 ͑Ref. 22͒ as well as piezoelectric properties.…”