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Structural evolution of the R‐T phase boundary in KNN ‐based ceramics
Author(s) -
Lv Xiang,
Wu Jiagang,
Xiao Dingquan,
Zhu Jianguo,
Zhang Xixiang
Publication year - 2018
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.15266
Subject(s) - phase boundary , tetragonal crystal system , materials science , orthorhombic crystal system , raman spectroscopy , ceramic , curie temperature , crystallography , phase (matter) , electromechanical coupling coefficient , piezoelectric coefficient , analytical chemistry (journal) , mineralogy , crystal structure , condensed matter physics , chemistry , composite material , physics , optics , organic chemistry , chromatography , ferromagnetism
Abstract Although a rhombohedral‐tetragonal (R‐T) phase boundary is known to substantially enhance the piezoelectric properties of potassium‐sodium niobate ceramics, the structural evolution of the R‐T phase boundary itself is still unclear. In this work, the structural evolution of R‐T phase boundary from −150°C to 200°C is investigated in (0.99− x )K 0.5 Na 0.5 Nb 1− y Sb y O 3 –0.01CaSnO 3 – x Bi 0.5 K 0.5 HfO 3 (where x = 0‐0.05 with y = 0.035, and y = 0‐0.07 with x = 0.03) ceramics. Through temperature‐dependent powder X‐ray diffraction ( XRD ) patterns and Raman spectra, the structural evolution was determined to be Rhombohedral (R, <−125°C)→Rhombohedral + Orthorhombic (R + O, −125°C to 0°C)→Rhombohedral + Tetragonal (R + T, 0 °C to 150°C)→dominating Tetragonal (T, 200°C to Curie temperature ( T C )) → Cubic (C, > T C ). In addition, the enhanced electrical properties (e.g., a direct piezoelectric coefficient ( d 33 ) of ~450 ± 5 pC/N, a conversion piezoelectric coefficient ( d 33 ∗ ) of ~580 ± 5 pm/V, an electromechanical coupling factor ( k p ) of ~0.50 ± 0.02, and T C ~250°C), fatigue‐free behavior, and good thermal stability were exhibited by the ceramics possessing the R‐T phase boundary. This work improves understanding of the physical mechanism behind the R‐T phase boundary in KNN ‐based ceramics and is an important step toward their adoption in practical applications.