The phase diagram of K_0.5Na_0.5NbO₃–Bi_1/2Na_1/2TiO₃

Abstract

The phase diagram of the lead-free piezoelectric (1 À x)K 0.5 Na 0.5 NbO 3 -xBi 1/2 Na 1/2 TiO 3 system has been studied by high-resolution synchrotron powder diffraction, neutron powder diffraction and selected area electron diffraction. The two lead-free piezoelectric materials K 0.5 Na 0.5 NbO 3 and Bi 1/2 Na 1/2 TiO 3 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 (Pm3m) 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 K 0.5 Na 0.5 NbO 3 -Bi 1/2 Na 1/2 TiO 3 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 ABO 3 structure at room temperature.

Remarkable impact of low BiYbO3 doping levels on the local structure and phase transitions of BaTiO3

“…From XRD data all ceramics appear isostructural, with identical average structure, therefore the dielectric behaviour may be associated to subtleties on the local structure. Similar subtleties were invoked by Liu et al 17 , 18 to explain the evolution of the dielectric properties in the K 0.5 Na 0.5 NbO 3 –Bi 0.5 Na 0.5 TiO 3 system. Those authors used both diffraction and Raman spectroscopy to obtain a better picture of the average vs. local structure.…”

Lead‐reduced Bi(Ni2/3Ta1/3)O3‐PbTiO3 perovskite ceramics with high Curie temperature and performance

“…The variation in the tetragonality c / a will be closely related to the variation in ferroelectric properties and Curie temperatures . Similar cases could be found in Bi(Ni 2/3 Ta 1/3 )O 3 ‐PbTiO 3 systems …”

Thermal evolution of polar nanoregions identified by the relaxation time of electric modulus in the Bi 1/2 Na 1/2 TiO 3 system

“…A possible mechanism explaining the longer-timeresponse of the PNRs is the side-ways motion of their boundaries without a change of orientation (just change volumes), [38] which should attribute to the distortion structure and heterovalent ions are displaced at both A site and B site in BNT-based ceramics. [39] The long relaxation time and the small change in them (10 -5~1 0 -2 s) in the studied temperature range suggest: (i) a mixture of the time response of the R3c and P4bm polarization mechanisms (ii) minor changes in the size of the PNRs [40] and (iii) large size of the PNRs. Our previous work [40][41][42] reported that a coexistence of R3c and P4bm phase was evident in BNT-KNN ternary systems.…”