Reduced degree of phase coexistence in KNN-Based ceramics by competing additives

Abstract

This work reveals the role of Bi3+ in the controlling ability of (Bi0.5Ag0.5)ZrO3 to the phase structure of potassium sodium niobate based ceramics by introducing Ba2+. The substitution on (Bi0.5Ag0.5)2+ with Ba2+ results in the reduced degree of phase coexistence, accompanying the phase transition from coexisting orthorhombic-tetragonal (O-T) phases to an orthorhombic (O) phase, which is demonstrated by the systematic phase structure analysis and variations of electrical properties. The analysis reveals that the high electronegativity of Bi3+ results in the increased covalent bond character and then increases the stabilization of the T phase, leading to a decrease in orthorhombic-tetragonal phase transition temperature (TO-T). Therefore, this work not only compares the controlling ability of Ba2+ and (Bi0.5Ag0.5)2+ to TO-T but also reveals which and how elements cause the decreased TO-T, promoting the understanding of the effect of additives on the phase structure.

The Role of Adding Bi0.5A0.5ZrO3 in Affecting Orthorhombic-Tetragonal Phase Transition Temperature and Electrical Properties in Potassium Sodium Niobate Ceramics

“…Next, we presented detailed evidence for the aforementioned analysis, studied the variations of electrical properties caused by these influences, and revealed their synergetic effects on reducing TO-T. We first measured the temperature-dependent relative permittivity (εr-T) to study the degree of diffuseness (i.e., γ) and further reveal the room-temperature phase structure (Figures 3(a-f which is consistent with the results from the room-temperature XRD patterns. Thus, Bi3+ does decrease TO-T, which coincides with our previous results [13]. Note that even though the secondary phase, the distinct TO-T is still observed in KNN-Zr (x = 0-0.04), KNNS-Bi (y = 0-0.005), and KNN-Bi (z = 0-8 0.01) ceramics (Figures 3 and S7), which explains why many studies still discussed the variations of TO-T and phase structure of KNN-based ceramics with secondary phases [38][39][40].…”

“…This explanation can extend to Bi-O bonds because Pb and Bi have the same extranuclear electron arrangement in 6s orbit (Pb: 6s26p2 and Bi: 6s26p3) [17,18]. Besides, the TO-T of KNN-based ceramics was reported to increase when replacing (Bi0.5Na0.5)2+ with other ions (e.g., Sr2+, Ca2+, Ba2+) that have a lower electronegativity than Bi3+, further proving the foregoing analysis [13,19,20]. In principle, aliovalent substitutions on A-site (K+/Na+) with Bi3+ shall destroy long-range ordering (LRO) and hinder grain growth [21].…”

“…We recently proved that the high electronegativity of Bi3+ is crucial for Bi0.5A0.5ZrO3 to decrease TO-T [13]. The high electronegativity of Bi3+ causes a higher covalent bond percentage in Bi-O bonds than K/Na-O bonds [3].…”

Alkali Niobate Powder Synthesis Using an Emerging Microwave-Assisted Hydrothermal Method

“…Sodium and potassium niobate K x Na 1− x NbO 3 (KNN)-based ceramics seem to be the most interesting piezoceramics to replace textured lead-based ones, the standard thanks to their highest piezoelectric features but causing an environmentally negative impact and human health unsafe behavior in use [ 4 , 5 , 6 , 7 , 8 ]. Ceramics based on KNN are secure from an environment point of view and show a promising combination of electro-mechanical properties and thermal stability [ 9 , 10 , 11 , 12 , 13 , 14 ]. However, the processing and sintering of such high-quality ceramics is still a challenge [ 15 ].…”

Outstanding Piezoelectricity of (K, Na)(Nb, Sb)O3-SrZrO3-(Bi, Ag)ZrO3 Piezoceramics and Their Application to a Planar-Type Actuator

“…Li + and Sb 5+ ions have also been used to develop such a multi-structure by transferring T O−R and T T−O to RT [18,[48][49][50]. Furthermore, the (Bi, Ag)ZrO 3 (BAZ) compound was also utilized to improve the piezoelectricity of KNN-related piezoceramics through the development of a multi-structure with nanodomains, and KNN-based piezoceramics with T-O-R, O-R, R-T, and T-O multi-structures were produced using the BAZ compound; they showed comparatively large d 33 values of 235-490 pC/N [47,[51][52][53]. Moreover, relaxor properties with nanodomains were also observed in the BAZ-added KNN-based piezoceramics.…”