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Dielectric and Electromechanical Properties of Zr-Doped BNT-ST Lead-Free Piezoelectric Ceramics
Amir Ullah,Mateen Ullah,Aman Ullah,A. V. Trukhanov,Ghulam Saddiq,Burhan Ullah,Aurang Zeb,Saeed Ullah Jan,김일원 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.6
0.72(Bi$_{0.5}$Na$_{0.5}$)Ti$_{(1-x)}$Zr$_x$O$_3$-0.28SrTiO$_3$ (BNTZ-ST) with $x$ = 0.00, 0.01, 0.02 and 0.03 were produced using a solid solution reaction procedure. Results from the X-ray diffraction (XRD) analysis showed the presence of a perovskite structure with cubic symmetry for all samples. Surface analysis was completed using field emission scanning electron microscopy (FE-SEM), and the grain size was found to decrease slightly with increasing Zr doping. The grain morphology was primarily rectangular, but morphed into a rounder shape with increases in Zr. In a dielectric constant study, the depolarization temperature was found to decrease with increasing Zr$^{+4}$ content and increasing frequency. The strain was found to be 0.34\% for the undoped samples with an equivalent dynamic strain ($S_{max}/E_{max}$) of 618 pm/V, without negative strain. However, the strain decreased slightly and hysteresis loops become slim and more symmetric, attaining a relaxor ferroelectric behavior with increasing Zr content.
Aman Ullah,Chang Won Ahn,Ali Hussain,Ill Won Kim 한국물리학회 2010 Current Applied Physics Vol.10 No.6
Lead-free Bi0.5(Na0.78K0.22)0.5TiO3 (BNKT) piezoelectric ceramics were synthesized by the solegel technique. The effects of sintering temperatures on the crystal structure, microstructure, densification,dielectric, ferroelectric and electric field-induced strain behaviors of the BNKT ceramics were investigated. X-ray diffraction patterns exhibited a pure perovskite structure from 1075 to 1150 ℃. A scanning electron microscopy study revealed an increase in grain size with increasing sintering temperature. The density of the ceramics sintered at 1150 ℃ reaches a maximum value of 5.55 g/㎤, which is 96% of the theoretical density. BNKT ceramics sintered at an optimum temperature of 1150 ℃ exhibited a high remnant polarization of 18.5 mC/㎠, a high electric field-induced strain of 0.20% and dynamic piezoelectric coefficient d33 * = (Smax/Emax) of 247 pm/V.
Aman Ullah,이선영,이해준,황학인,Ali Hussain,이재신,김일원,안창원 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.41
Lead-free piezoelectric (1 - x)(Bi0.5(Na0.75K0.25)0.5TiO3)-xBiAlO3 (BNKT25-BA, 0 ≤ x ≤ 0.10)ceramics were synthesized using a conventional solid state reaction method. The incorporation of BA into the BNKT25 lattice was investigated by using X-ray diffraction (XRD), ferroelectric characterizations and electric-field-induced strain behavior. X-ray diffraction revealed a pure perovskite phase for x ≤ 0.050. A phase transformation from tetragonal to pseudocubic was observed at x =0.050. The polarization hysteresis loops of the BNTK25-BA ceramics indicate that the addition of BA significantly disrupts the ferroelectric order of BNKT25 ceramics. The destabilization of the ferroelectric order is accompanied by an enhancement of the unipolar strain. In particular, a large electric-field-induced strain (S = 0.29%) and a normalized strain (d*33 = Smax/Emax = 484 pm/V)were observed at x = 0.025, near the tetragonal-pseudocubic phase boundary. These results suggest that the BNKT25-BA system is a promising candidate for lead-free electromechanical applications.
Aman Ullah,안창원,Ali Hussain,Hai Joon Lee,Ill Won Kim,이선영 한국물리학회 2010 Current Applied Physics Vol.10 No.4
Lead-free piezoelectric (1 - x)(Bi0.5(Na0.78K0.22)0.5TiO3)–xBiAlO3 (abbreviated BNKT22–BA, x = 0.00–0.100)ceramics were synthesized using a conventional sintering technique. The incorporation of BA into the BNKT22 lattice was investigated by X-ray diffraction (XRD), and the dielectric and ferroelectric characterizations and electric field-induced strain behavior. Wefound that the structural and electrical properties of BNKT22 ceramics are significantly influenced by the presence of BA content. X-ray diffraction revealed a pure perovskite phase for x ≤ 0.050. A phase transformation from tetragonal to pseudocubic was observed at x = 0.050. As BA content increased, the maximum dielectric constant continuously decreased, and the depolarization temperature (Td) shifted towards lower temperatures. The polarization and strain hysteresis loops indicate that the addition of BA significantly disrupts the ferroelectric order. The destabilization of the ferroelectric order is accompanied by an enhancement of bipolar and unipolar strains. In particular,a very large electric field-induced strain (S = 0.35%) and a normalized strain (d*33 = Smax/Emax = 592 pm/V)were observed at x = 0.030, near the tetragonal–pseudocubic phase boundary. These results suggested that the BNKT22–BA system is a promising candidate for high performance, lead-free electromechanical applications.
AMAN-ULLAH, Attia,AZIZ, Azelin,IBRAHIM, Hadziroh Korea Distribution Science Association 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.3
This study aims to investigate the impact of workplace safety on doctors' retention and turnover intention along with job satisfaction as the mediator. A questionnaire-based survey was conducted with 394 medical doctors working in thirty-five hospitals in Pakistan using a structural equation modeling. Results of the study showed that: 1) workplace safety has a significant positive relationship with employee retention; 2) workplace safety has a significant negative relationship with turnover intention; 3) workplace safety has a significant positive relationship with job satisfaction; 4) job satisfaction has a significant positive relationship with employee retention; 5) job satisfaction has a significant positive relationship with turnover intentions; 6) job satisfaction mediates between workplace safety and employee retention; while 7) job satisfaction failed to mediate between workplace safety and turnover intentions. The findings of the study suggest that in a fear-free and safe environment, employees' chance to stay will increases. The study also suggests that dissatisfied employees do not need to leave the organization. There can be other factors that can be explored in future studies. This study also provides a practical implication for the doctors' low retention and high turnover, specifically in the healthcare sector of Pakistan by providing guidelines to the human resource executives to focus on the strategic implementation of workplace safety.
Shakir Ullah,Usman Khan,Khalil Ur Rahman,Aman Ullah 경남대학교 극동문제연구소 2021 ASIAN PERSPECTIVE Vol.45 No.4
This study provides a critical literature review of the benefits and problems associated with one of the largest Chinese- funded development projects, the China-Pakistan Economic Corridor (CPEC), with particular focus on the implications of this project for local people in Pakistan. CPEC is one of the most significant development projects in Pakistan, covering infrastructure, agriculture, and energy cooperation. Although some studies have examined challenges and problems brought about by CPEC, the majority of them fail to examine specific localities and the Pakistani communities that have been impacted by the project. Hence, most of the investigations have reported general development impacts rather than indicating whether and how CPEC has brought either benefits or problems to local people. In examining previously published studies on CPEC, this essay highlights gaps in research, especially from anthropological and sociological perspectives, with the goal of encouraging further studies from the vantage point of the local communities regarding development projects in Pakistan.