Rizwan Ahmed Malik

Structure–property relationship in lead-free A- and B-site co-doped Bi0.5(Na0.84K0.16)0.5TiO3–SrTiO3 incipient piezoceramics

In this work, a phase diagram of A- and B-site co-substituted 0.96[{Bi0.5 (Na0.84K0.16)}1−x−yLixMgy(Ti1−zNbz)O3]–0.04SrTiO3 (abbreviated as LMN-doped BNKT–ST), where x, y and z = 0.00–0.030, was schematically constructed on the basis of crystal structure and electromechanical, dielectric and piezoelectric properties. The underlying mechanism of the compositionally-induced non-ergodic (NR) to ergodic relaxor (ER) phase transition was explored, and emphasis was given on relating the chemically-induced polymorphic structural phase transition to the dynamics of polar nano-regions (PNRs) and their random fields, which strongly affect the dielectric, ferroelectric, piezoelectric and field-induced strain properties of the investigated system. X-ray diffraction patterns revealed that LMN doping resulted in a transition from coexistence of rhombohedral and tetragonal phases to a pseudocubic phase. Both the dielectric constant and the ferroelectric–relaxor transition (TF–R ∼ 100 °C) temperature decreased with an increase in LMN content. The piezoelectric and ferroelectric responses of the BNKT–ST ceramics were significantly decreased by the addition of LMN. However, the destabilization of the piezoelectric and ferroelectric properties was accompanied by significant enhancements in the bipolar and unipolar strains. A large electric-field-induced strain (S = 0.28%) and a corresponding dynamic piezoelectric constant (Smax/Emax) of 560 pm V−1 were observed under the driving field of 5 kV mm−1 when 1.5 mol% LMN was substituted on respective sites. This significant strain enhancement at this composition, with LMN = 0.015, may be attributed to both the field-induced reversible structural transition and the compositionally-induced NR to ER phase transition. The composition- and temperature-dependence of the energy storage density (W) were studied to demonstrate the practicability of the LMN-doped BNKT–ST. It was found that the addition of LMN enhanced the difference between maximum polarization and remnant polarization, resulting in an improvement of the energy storage properties. For the composition with LMN = 0.020, a nearly temperature-invariant large recoverable energy density (W = 0.70 J cm−3) was achieved under 5.5 kV mm−1 in the wide temperature range of 100–150 °C. These properties indicate that the synthesized system might be a promising lead-free candidate for actuator and energy storage capacitor applications.

Dielectric and electromechanical properties of LiNbO3-modified (BiNa)TiO3-(BaCa)TiO3 lead-free piezoceramics

The dielectric and electromechanical properties of LiNbO3-modified (1–x) [0.91Na0.5Bi0.5TiO3–0.09Ba0.70Ca0.30TiO3]–xLiNbO3 (abbreviated as (BiNa)TiO3–(BaCa)TiO3–LN) lead-free piezoceramics were investigated. The electrical properties revealed that the addition of LiNbO3 (LN) induces a phase transition from a non-ergodic relaxor to an ergodic relaxor in the (BiNa)TiO3–(BaCa)TiO3–LN system. A large electrostrain of ~0.418% with a normalized strain of ~690 pm V−1 at 6 kV mm−1 was observed at the coexistence of the non-ergodic relaxor and ergodic relaxor phases for LN 0.020, where a field-assisted reversible phase transition between metastable ferroelectric and stable ergodic relaxor phases occurs. Subsequently, a gradual enhancement in the temperature stability of the dielectric constant was observed. At 3 mol.% LN, a nearly constant temperature and a frequency-invariant permittivity of e r ~ 3300 over a broad temperature range of 147 °C–306 °C was observed along with small losses from room temperature up to 400 °C.

Dielectric and Ferroelectric Properties of Nb Doped BNT-Based Relaxor Ferroelectrics

The effects of Nb doping on the crystal structure, microstructure, and dielectric ferroelectric and piezoelectric properties of (BNBTNb-SZ, with

Enhanced Piezoelectric Properties of Lead-Free La and Nb Co-Modified Bi0.5(Na0.84K0.16)0.5TiO3-SrTiO3 Ceramics

{\chi}

Structural, Ferroelectric and Field-Induced Strain Response of Nb-Modified (Bi0.5Na0.5)TiO3-SrZrO3 Lead-Free Ceramics

New lead-free piezoelectric ceramics 0.96[{Bi0.5 (Na0.84 K0.16)0.5}1-xLax(Ti1-y Nby)O3]-0.04SrTiO3 (BNKT-ST-LN, where x = y = 0.00 ≤ (x = y) ≤ 0.015) were synthesized using the conventional solid-state reaction method. Their crystal structure, microstructure, and electrical properties were investigated as a function of the La and Nb (LN) content. The X-ray diffraction patterns revealed the formation of a single-phase perovskite structure for all the LN-modified BNKT-ST ceramics in this study. The temperature dependence of the dielectric curves showed that the maximum dielectric constant temperature (Tm) shifted towards lower temperatures and the curves became more diffuse with an increasing LN content. At the optimum composition (LN 0.005), a maximum value of remnant polarization (33 C/cm2) with a relatively low coercive field (22 kV/cm) and high piezoelectric constant (215 pC/N) was observed. These results indicate that the LN co-modified BNKT-ST ceramic system is a promising candidate for lead-free piezoelectric materials.

Structural and electromechanical properties of Na0.5Bi0.5TiO3 ceramics produced by different synthesis routes

Lead-free ceramics system of 0.96[Bi0.5Na0.5Ti(1−x)NbxO3]-0.04SrZrO3 BNT-SZ-Nb100x (with Nb100x = 0–4) were prepared by a solid-state reaction method. X-ray diffraction analysis revealed the formation of pure perovskite phase with x ≤ 0.03. The temperature dependence of dielectric curves showed that maximum dielectric constant temperature (Tm) shifted towards lower temperatures and the curves become more diffuse with increasing Nb doping. Ferroelectric curves indicated a disruption of ferroelectric order upon Nb addition. From Nb0 to Nb2 ceramics, maximum values for the field-induced strain (Smax) was enhanced from 0.09 to 0.22%. The corresponding normalized strain (Smax/Emax) was increased from 125 to 315 pm/V.

Structural and dielectric properties of La and Nb co-substituted Bi 0.5 (Na 0.84 K 0.16 ) 0.5 TiO 3 -SrTiO 3 ceramics

Sodium bismuth titanate, Na0.5Bi0.5TiO3 (NBT) ceramics were produced by three different methods; conventional mixed-oxide (CMO) route, molten salt synthesis (MSS) and topochemical microcrystal conversion (TMC) and then sintered at 1150 oC for 2 h in air atmosphere. The crystal structure, dielectric, ferroelectric and field-induced strain properties were investigated for all samples. All samples showed a single phase perovskite structure without any evidences of unwanted secondary phases. The NBT ceramics synthesized by the TMC method show slightly better dielectric, ferroelectric and field induced strain response as compared with CMO and MSS synthesized ceramics. The room temperature dielectric constant measured at 1 kHz increased from 218 for NBT ceramics synthesized by MSS method to 271 and 330 for CMO and TMC synthesized ceramics, respectively. Similarly, the dynamic piezoelectric coefficient (d 33*) enhanced from 91 pm/V for CMO synthesized to 97 pm/V and 107 pm/V for MSS and TMC synthesized ceramics, respectively.

Temperature‐Insensitive High Strain in Lead‐Free Bi0.5(Na0.84K0.16)0.5TiO3–0.04SrTiO3 Ceramics for Actuator Applications

In this article La and Nb co-substitution effect on the crystal structure, microstructure, ferroelectric and dielectric properties of 0.96[{Bi_0.5 (Na_0.84 K_0.16)_0.5}_1-xLa_x(Ti_1-y Nb_y)O₃]-0.04SrTiO₃ (BNKLTN-ST, where (x=y) = 0.00 - 0.020) ceramics has been investigated. The ceramics with x,y ≤ 0.010 have pure perovskite structure, while a secondary phase appears in the sample with x=y = 0.020. X-ray diffraction patterns revealed that La and Nb co-doping resulted in a transition from coexistent rhombohedral and tetragonal phases to pseudocubic symmetry. The co-doping of La and Nb slightly increased the average grain size. The maximum permittivity temperature (T_m) increased with increasing La and Nb contents, but the values of depolarization temperature (T_d) as well as maximum dielectric constant (ε_m) decrease gradually. La and Nb addition interrupted the polarization and reveals that the ferroelectric (FE) order of unmodified BNKT-ST ceramics lead to a declination of remnant polarization along with coercive field. The results shows that La and Nb co-doping into BNKT-ST ceramics induces a phase transition from relaxor FE to ergodic relaxor phase with a substantial deterioration of the long-range FE order.