Terahertz Probing Irreversible Phase Transitions Related to Polar Clusters in Bi_0.5Na_0.5TiO₃‐Based Ferroelectric

Abstract

ferroelectric materials, which are comprised of non-centrosymmetric unit cells, each possessing a switchable polarization of their electric dipole moment. Of the class of ferroelectric materials, perovskitestructured Bi 0.5 Na 0.5 TiO 3 (BNT)-based compounds have attracted worldwide research interest in recent years with the development of lead-free forms, [4] which have been deployed in a range of technological applications, including piezoelectric actuators, sensors, and dielectric capacitors. Each of these areas of utility is respectively attributed to their large electric field-induced strain, [5] high piezoelectric constant, and high specific energy. While earlier studies of the crystal structure and phase transitions of BNT have answered many questions, there still remain some key points that are controversial due to the complexity of NaO and BiO bonds, and the octahedral tilt in the unit cell. [6] Due to these unique structural properties, phase transitions in BNT, and its derivatives, can be induced by applied electric fields of 10s of kV cm −1 [7,8] which, in most cases, are indirectly represented by the electrical field-dependent bipolar current, polarization, or strain loops Electric-field-induced phase transitions in Bi 0.5 Na 0.5 TiO 3 -based relaxor ferroelectrics are essential to the control of their electrical properties and consequently in revolutionizing their dielectric and piezoelectric applications. However, fundamental understanding of these transitions is a long-standing challenge due to their complex crystal structures. Given the structural inhomogeneity at the nanoscale or sub-nanoscale in these materials, dielectric response characterization based on terahertz (THz) electromagnetic-probe beam fields is intrinsically coordinated to lattice dynamics during DC-biased poling cycles. The complex permittivity reveals the field-induced phase transitions to be irreversible. This profoundly counters the claim of reversibility, the conventional support for which is based upon the peak that is manifest in each of four quadrants of the current-field curves. The mechanism of this irreversibility is solely attributed to polar clusters in the transformed lattices. These represent an extrinsic factor, which is quiescent in the THz spectral domain.

Multiscale understanding of electric polarization in poly(vinylidene fluoride)-based ferroelectric polymers

“…3d-f) and can be used as a reference for the phase identification of PVDF-based materials. 25 The loss peak at about 1.50-1.60 THz is a libration lattice mode in a-PVDF. The peaks at B0.63 THz and 2.10 THz are generally considered as b-characteristic, which arises from the librational lattice mode around the polymer chain c-axis and the pure translation along the crystallographic a-axis.…”

“…, P s and LP contribute to the dielectric properties of PVDF-TrFE at high frequencies. 25 The extruded PVDF-TrFE films were chosen as a model to describe the structure and polarization specifications since they crystallize into oriented b-phase crystals (Fig. 4) and displays lamellae bundle morphology at micro-meter scale, as evidenced by SEM image (Fig.…”

Ultrasound‐Driven Non‐Metallic Fenton‐Active Center Construction for Extensive Chemodynamic Therapy

“…Based on the common characteristic of Fenton/Fenton-like catalysts, which is the capability of facilitating electron transfer to cleave the peroxide bond (O-O), the material systems applied in CDT can be extended beyond transition metals or metal oxides. Utilizing the piezoelectric nature of BNT-based materials, [12] the external periodic pressure induced by ultrasound (US) causes a polarization change, thereby establishing a built-in electric field across the material [13] which drives free charge carriers (electrons and holes) to opposite ends of the materials, as shown in the reaction BNT + US → BNT (e − + h + ). Notably, the separated charge carriers could synchronize the oxidation of H 2 O and the reduction of H 2 O 2 to increase •OH yield (Figure 1a), which is significant in the case of low 1b).…”

Terahertz probing of low‐temperature degradation in zirconia bioceramics

“…Previously, THz technology has been used to analyze biomolecules and biomaterials as it can stimulate low‐energy processes such as intra‐ and intermolecular vibrations 15–18 . THz radiation is accessible to a variety of physical properties of ceramics, such as complex refractive index and complex dielectric permittivity, making it possible to probe phase transitions of polar ceramics by the simultaneous measurement of the temperature dependencies of the dielectric permittivity and dielectric loss 19,20 . However, in bioceramics, the application of THz technology has been rarely reported.…”