Improved ferroelectric/piezoelectric properties and bright green/UC red emission in (Li,Ho)-doped CaBi₄Ti₄O₁₅ multifunctional ceramics with excellent temperature stability and superior water-resistance performance

Abstract

Multifunctional materials based on rare earth ion doped ferro/piezoelectrics have attracted considerable attention in recent years. In this work, new lead-free multifunctional ceramics of Ca1-x(LiHo)x/2Bi4Ti4O15 were prepared by a conventional solid-state reaction method. The great multi-improvement in ferroelectricity/piezoelectricity, down/up-conversion luminescence and temperature stability of the multifunctional properties is induced by the partial substitution of (Li0.5Ho0.5)(2+) for Ca(2+) ions in CaBi4Ti4O15. All the ceramics possess a bismuth-layer structure, and the crystal structure of the ceramics is changed from a four layered bismuth-layer structure to a three-layered structure with the level of (Li0.5Ho0.5)(2+) increasing. The ceramic with x = 0.1 exhibits simultaneously, high resistivity (R = 4.51 × 10(11)Ω cm), good piezoelectricity (d33 = 10.2 pC N(-1)), high Curie temperature (TC = 814 °C), strong ferroelectricity (Pr = 9.03 μC cm(-2)) and enhanced luminescence. These behaviours are greatly associated with the contribution of (Li0.5Ho0.5)(2+) in the ceramics. Under the excitation of 451 nm light, the ceramic with x = 0.1 exhibits a strong green emission peak centered at 545 nm, corresponding to the transition of the (5)S2→(5)I8 level in Ho(3+) ions, while a strong red up-conversion emission band located at 660 nm is observed under the near-infrared excitation of 980 nm at room temperature, arising from the transition of (5)F5→(5)I8 levels in Ho(3+) ions. Surprisingly, the excellent temperature stability of ferroelectricity/piezoelectricity/luminescence and superior water-resistance behaviors of piezoelectricity/luminescence are also obtained in the ceramic with x = 0.1. Our study suggests that the present ceramics may have potential applications in advanced multifunctional devices at high temperature.

Enhanced electrical properties in W/Cu co‐doped CaBi2Nb2O9 high‐temperature piezoelectric ceramics

“…It is known that changes in T C for ferroelectrics that contain the perovskite cell depend closely on the tolerance factor ( t ). The formula for the tolerance factor ( t ) is as follows:where r A , r B , and r O are the ionic radii of the A‐site cation, B‐site cation, and oxygen ion, respectively 27,28 . A smaller t value usually corresponds to a larger T C for CBN‐based ceramics 29,30 .…”

“…where r A , r B , and r O are the ionic radii of the A-site cation, B-site cation, and oxygen ion, respectively. 27,28 A smaller t value usually corresponds to a larger T C for CBN-based ceramics. 29,30 Replacing Nb 5+ (0.64 Å) with the smaller W 6+ /Cu 2+ ions (average ionic radii 0.6325 Å) could cause an increase in the tolerance factor, and this might account for the decrease in…”

Effect of (K0.5Ce0.5) complex on the electrical properties of lead‐free Bi4Ti2.86W0.14O12 high‐temperature piezoelectric ceramics

“…A phase transition from ferroelectric to paraelectric corresponding to T C is observed at 632 o C for pure BITW ceramics. With the increase of (K 0.5 Ce 0.5 ) complex doping amount from x = 0 to x = 0.1, the dielectric constant peak value at T C is slightly suppressed and the T C is found to be gradually decreased to 608 o C. Generally, the transition temperature from ferroelectric to paraelectric phase is closely related to the orthorhombic distortion of BLSFs, which can be described by the tolerance factor t of the (A m−1 B m O 3m+1 ) 2− pseudoperovskite unit according to the following equation [36,37,38]:…”

Effect of La3+ substitution on the physical properties of CaTiO3–0.15KNbO3-based lead-free ceramics

“…To explain the overall compactness, stability and the existence of distortions in the perovskite structure, Goldschmidt suggests a tolerance factor (t) which is expressed by the following relation [18]: where ⟨r A ⟩ , ⟨r B ⟩ and r O are the ionic radii [19]. The perovskite structure only exists if 0.75 ≤ t ≤ 1.06 and, depending on its value, more or less distorted cubic structures are observed.…”