Adnan Maqbool

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.

Ferroelectric and piezoelectric properties of SrZrO3-modified Bi0.5Na0.5TiO3 lead-free ceramics

Abstract The lead-free SrZrO 3 -modified Bi 0.5 Na 0.5 TiO 3 (BNT-SZ100 x , with x= 0–0.15) ceramics were fabricated by a conventional solid-state reaction method. The effects of SZ addition on BNT ceramics were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), ferroelectric and electric field-induced strain characterizations. XRD analysis revealed a pure perovskite phase without any traces of secondary phases. Ferroelectric and bipolar field induced-strain curves indicated a disruption of ferroelectric order upon SZ addition into BNT ceramics. A maximum value of remnant polarization (32 µC/cm 2 ) and piezoelectric constant (102 pC/N) was observed at 5% (mole fraction) of SZ. Maximum value of the electric field-induced strain ( S max =0.24%) corresponding to normalized strain ( S max / E max = d * 33 = 340 pm/V) was obtained at BNT-SZ9.

Mechanical properties of CNT reinforced hybrid functionally graded materials for bioimplants

Abstract The hybrid functionally graded materials (FGM) of hydroxyapatite (HA), stainless steel 316L (SS316L) and carbon nanotubes (CNT) were synthesized for biomedical implants. Three different types of FGM were produced by the combination of SS316L and CNT to reinforce HA in discrete layers of FGM. In the first type of FGM, concentration of SS316L was varied from 10% to 40% (mass fraction) with an increment of 10% to reinforce micro HA. In the second type of FGM, 0.5% (mass fraction) functionalized CNT was added by maintaining the rest of composition as that of the first type of FGM. In the third type of FGM, mixture of micro and nano HA (mass ratio1:1) was used, keeping rest of composition similar to the second type of FGM. All types of FGM were subjected to uniaxial compaction and sintered by pressureless sintering technique at similar compaction and sintering parameters. The results show that the densification is enhanced with the addition of CNT and nanocrystalline HA in the FGM. Hardness and fracture toughness increase in both FGM reinforced with CNT, but the increase of the hardness and fracture toughness are more pronounced in FGM with micro and nanocrystalline HA.

Structure and temperature dependent electrical properties of lead-free Bi0.5Na0.5TiO3- SrZrO3 ceramics

Lead-free SrZrO3-modified Bi0.5Na0.5TiO3 (BNT-SZ) ceramics were fabricated by a conventional solid state reaction method. X-ray diffraction analysis reveals a pure perovskite phase without any traces of secondary phases. Scanning electron microscopy images depicts dense grain morphology. The temperature dependences of the dielectric behavior was measured in the temperature range of 50-500 °C at 100 kHz. With the increase in SZ content, the dielectric constant (er) constantly decreased and the maximum dielectric constant temperature (Tm) shifted towards lower temperatures. In addition to this, ferroelectric hysteresis loops indicated a disruption of ferroelectric order and increase in the relaxor character of BNT ceramics with increase in SZ concentration. A maximum values of remnant polarization (32 μC/cm2) and piezoelectric constant (100 pC/N) were observed at SZ5 and SZ4, respectively.

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

Synthesis of copper coated carbon nanotubes for aluminium matrix composites

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Impedance Spectroscopy of Sodium Excess Ta-Modified (K0.5Na0.5)NbO3 Ceramics Prepared by Reactive Templated Grain Growth

In this investigation copper coated carbon nanotubes (CNTs) were prepared to enhance the interfacial bonding between CNTs and aluminum matrix by the molecular-level mixing process. In optimized plating bath of (1:1) by wt. CNT with Cu, thickness of coated CNTs is reduced to 100 nm to promote uniform distribution of Cu nanoparticle on the surface of pretreated CNTs. The mixing of CNTs was accomplished by ultrasonication and ball milling. Scanning electron microscope analysis revealed the homogenous dispersion of Cu-coated CNTs in nanocomposites samples compared to the uncoated CNTs. The samples were pressureless sintered under vacuum. The densification increased with the increase in the CNTs content and is more pronounced in Cu-coated CNT nanocomposites.

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

Polycrystalline, sodium excess Ta-modified (K0.470Na0.545)(Nb0.55Ta0.45)O3 ceramics were synthesized by reactive templated grain growth method. The crystal structure and microstructure of the synthesized (K0.470Na0.545)(Nb0.55Ta0.45)O3 ceramics were examined with X-ray diffraction and scanning electron microscopy. Complex impedance spectroscopy measurements have been carried out to investigate electrical properties in wide frequency range (0.1 Hz – 1 MHz) at different temperatures. Contributions from grain boundaries and from the grain interiors can be distinguished in the complex impedance plots. Moreover, (K0.470Na0.545)(Nb0.55Ta0.45)O3 ceramics were found to exhibit negative temperature coefficient of resistance.

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.