Giant electrostrictive coefficient in rapidly cooled nanodisordered KTa1−xNbxO3 lead-free single crystals

Abstract

The temperature dependent electrostrictive effect, with respect to increasing the cooling rate to a cooling temperature, was quantitatively investigated in potassium tantalate niobate (KTN) lead-free single crystals above and near Curie temperature (TC). High work-function Pt electrodes are used to minimize the effect of charge injection, and the electric field induced displacement was measured with Michelson interferometry. It was found that a giant electrostrictive coefficient of 696 × 10−16 m2/V2 could be obtained at a high cooling rate of 0.75 °C/s to a temperature of TC + 4.5 °C due to the evolution of polar nano-regions, which is one order of magnitude larger than the previously reported value in KTN crystals. This strengthens the realization of replacing toxic lead-based electrostrictive materials with environmentally friendly KTN materials in real world applications.

Domain Engineering Enabled Giant Linear Electro‐Optic Effect and High Transparency in Ferroelectric KTa1−xNbxO3 Single Crystals

“…[37] However, increasing the temperature above T B does not seem to be required for the formation of PNRs. [5,38,39] A rapid decrease (a cooling rate of 1:67 C s À1 in our case) from T c þ 58 C (T > T Ã ) to T c þ 8 C (T > T c ) further restricts these partially reoriented Nb ions and displace Ta ions from their high symmetry sites at a rapid pace. As a result, These partially dynamic PNRs must rapidly stabilize into static PNRs to grow, further correlate and influence each other.…”

“…[ 37 ] However, increasing the temperature above does not seem to be required for the formation of PNRs. [ 5,38,39 ]…”

“…[ 40–42 ] This rapid stabilization affects the number and quenches the size of these static PNRs, which in turn develops quenched PNRs [ 7,43,44 ] that can affect other properties of the crystal. [ 5,38,39,45 ] These PNRs form with faceted boundaries and high anisotropic properties [ 46,47 ] could serve as effective seeds (the source of critical nucleation) for a process similar to abnormal grain growth (AGG) or an AGG‐like process. [ 48,49 ] During the slow cooling process from to any temperature below TC (from to in our case) at a cooling rate of , PNRs grow to form a macroscopic single domain ferroelectric crystal via an AGG‐like process [ 48 ] and achieve high transparency.…”

“…Furthermore, the polarizability of for relaxor ferroelectrics like KTN single crystals is affected by the cooling rate. [ 4,5,7,44 ] As the PNRs formed during the rapid cooling stage of our DE process (i.e., Process 1, as depicted in Figure 4) are quenched, they become smaller in size compared to its slowly cooled equivalent (i.e., Process 2, as depicted in Figure 4). As a result, the finalized individual size of each dipole moment in process 1 should be smaller than that in process 2.…”

“…Although potassium tantalate niobate [() KTN] single crystals have been initially grown and investigated over five decades ago, there still have been continuous efforts in exploring their large electro‐optic (EO) and electrostrictive properties and device applications. [ 1–3 ] Recent improvements in the growth and crystal quality of KTN have supported the development of nano‐disordered KTN crystals, which have substantially improved material properties such as the enhanced quadratic EO coefficient [ 4 ] and electrostrictive coefficient, [ 5 ] and have revealed unconventional material properties such as giant refraction. [ 6 ] These findings assisted in the discovery of new physical phenomena such as diffraction‐less free space light propagation by using its giant quadratic electro‐optic coefficient; [ 7 ] and the development of many useful optical/electro‐optic devices such as wide‐angle fast‐speed solid‐state EO beam deflectors via space‐charge‐controlled gradient electric field [ 8–12 ] and broadband‐free space switches and modulators.…”