Emergence of short-range polar order in relaxor ferroelectrics from a long-range ferroelectric order of Pb-free morphotropic phase boundary ceramics viz., K0.5Na0.5NbO3

Abstract We have explored long/short-range structure and dielectric property of K 0.5 Na 0.5 NbO 3 (KNN50) doped Ba 0.9 Sr 0.1 TiO 3 (BST10) ceramics viz., (1-x)KNN50-xBST10 (KBSTx) for 0.00 ≤ x ≤ 0.20. The combined analysis of composition-dependent X-ray diffraction and Raman scattering data demonstrates the emergence of short-range polar order (having monoclinic symmetry) in relaxor ferroelectrics (observed for x = 0.20 [Appl. Phys. Lett. 125, 102901 (2024)]) from a long-range ferroelectric order (observed for x < 0.20). A two-phase coexistence (i.e., monoclinic with Pm space group and tetragonal with P4mm space group) with a relatively high dielectric constant is observed for x = 0.05 (KBST5) in the ferroelectric region (0.00 ≤ x < 0.20). Moreover, the room temperature dielectric constant of KBST5 is found to be greater than adjacent compositions viz., KNN50 and KBST10 by 62% and 83%, respectively. Further, the composition-dependent frozen phonon mode analysis of KBSTx ceramics demonstrates that the maximum amplitude is observed at KBST5. This suggests a morphotropic phase boundary-like behavior for KBST5, highlighting its scientific and technological importance for diverse applications viz., energy harvesting, ferroelectric RAMs, electrocaloric devices, neuromorphic computing, etc.