Enhanced electrical properties and conduction mechanism of A-site rare-earth Nd-substituted CaBi₂Nb₂O₉

Abstract

Calcium bismuth niobate (CaBi2Nb2O9, CBN) is considered to be one of the most promising high-temperature piezoelectric materials owing to its high Curie temperature of ~940 ℃, however, its low electrical resistance and poor piezoelectric properties at elevated temperatures limit its applications at high temperatures. In this work, we report the significantly enhanced dc electrical resistivity and piezoelectric performance of CBN ceramics through rare-earth Nd-substitution. The crystal structure, microstructure, and dielectric, electrical, and piezoelectric properties of the Nd-modified CBN with nominal compositions of Ca1-xNdxBi2Nb2O9 (CBN-100xNd) have been investigated in detail. The results indicate that the substitution of Nd3+ ions for Ca2+ ions increases the piezoelectric properties, and reduces the dielectric loss tanδ at high temperatures. The dc and ac conduction mechanisms indicate that the conduction mechanism is closely related to oxygen vacancies that are reduced through the donor substitution of Nd3+ for Ca2+, thereby resulting in a significant improvement in the dc electrical resistivity. The optimal composition of CBN-3Nd exhibits a high piezoelectric constant d33 of 13.5 pC/N, and a high Curie temperature Tc of 948 °C. More importantly, the CBN-3Nd exhibits good thermal stability of the electrical properties (ρ=2.6 × 107·Ω cm at 500 °C and 1.8 × 106 Ω·cm at 600 °C, kp=6.17% at 500 °C), which demonstrates that the Nd-modified CBN ceramics are promising piezoelectric materials for use in high-temperature piezoelectric sensors.

Superior piezoelectricity and resistivity in CaBi2Nb2O9 high-temperature piezoelectric ceramics: synergy of structural distortion and weak texturing

“…5(b). 35,44,[47][48][49][50][51][52][53][54][55] Obviously, the T C , d 33 , r and tan d of CBNO ceramics obtained by adding the B 2 O 3 sintering aid in this work are very noticeable among these bulk samples and are comparable to those of most commercial piezoelectric single crystals at high temperatures. Specifically, an ultra-high electrical resistivity of 1.4 Â 10 7 O cm (at 600 1C), the largest value among the CBNO-based ceramics until now, as well as an ultrahigh T C of 958 1C and a rather high d 33 of 20.4 pC N À1 for CBNO-based ceramics have been achieved.…”

High‐performance bismuth titanate‐ferrite (Bi5Ti3FeO15) for high‐temperature piezoelectric applications

“…Figure 5A shows the dc electrical resistivity ( ρ dc ) of the BTF‐100 x W ceramics as a function of temperature, wherein it can be seen that the ρ dc value decreases as the temperature increases from 200 to 500°C, indicating that the charge carriers are thermally activated with a negative temperature coefficient of resistance 41 . Meanwhile, it is noted that the ρ dc values of the BTF‐100 x W samples were significantly higher than that of the pure BTF.…”

Origin of strong piezoelectric enhancement in bismuth titanate‐ferrite for high‐temperature applications

“…39 The modes at 544 and 572 cm −1 are attributed to the opposite vibration of the apical O atoms at the top of (Ti/FeO 6 octahedra, and the mode at 860 cm −1 is originated from the stretching vibration of (Ti/Fe)O 6 octahedra. 40 These modes in dash boxes 42 which makes the main intrinsic contribution to the enhancement of piezoelectric response. 43 Figure 2A-C shows the SEM images of the natural surface of Bi 5 Ti 3 FeO 15 , BTF-8Eu, and BTF-15Eu, respectively.…”

“…On the other hand, the calculated lattice parameters a and b decrease from 5.4638 and 5.4347 Å to 5.4523 and 5.4283 Å as the europium content increases from 0 to 0.15. The increased rotation angles and the decreased a / b ratio indicate an enhanced tetragonal lattice distortion in europium‐substituted Bi 5 Ti 3 FeO 15 , 42 which makes the main intrinsic contribution to the enhancement of piezoelectric response 43 …”

“…(D) Elemental distribution of BTF-8Eu. Note that the grain size is the grain length (the average diameter of plate-like grains) in the direction perpendicular to the c-axis.thereby enhancing the electrical properties of europiumsubstituted Bi 5 Ti 3 FeO 15 42. As shown in Figure2D, all the elements (O, Bi, Ti, Fe, and Eu) are homogeneously distributed in the grains and at the grain boundaries, indicating that the substitution of europium has incorporated into the crystal lattice of Bi 5 Ti 3 FeO 15 .…”