Amir Ullah
University of Ulsan
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Publication
Featured researches published by Amir Ullah.
Applied Physics Letters | 2013
Aman Ullah; Chang Won Ahn; Amir Ullah; Ill Won Kim
In this letter, the composition and electric field dependent strain behavior of (1 − x)Bi0.5(Na0.78K0.22)0.5TiO3-xBi(Mg0.5Ti0.5)O3 (BNKT-BMT) were investigated to develop lead-free piezoelectric materials with a large strain response at a low driving field for actuator applications. A large strain of 0.35% (Smax/Emax = 636 pm/V) at an applied field of 55 kV/cm was obtained with a composition of 4 mol. % BMT. In particular, the electric field required to deliver large strains was reduced to a level that revealed not only a large Smax/Emax of 542 pm/V at a driving field as low as 35 kV/cm, but also remarkably suppressed the large hysteresis.
RSC Advances | 2014
Laxman Singh; Ill Won Kim; Byung Cheol Sin; K. D. Mandal; U. S. Rai; Amir Ullah; Hoeil Chung; Youngil Lee
A facile way for the synthesis of nano-crystalline CaCu2.90Zn0.10Ti4O12 (CCZTO) using a solution combustion technique based on the glycine–nitrate process with inexpensive solid TiO2 powder as the raw material is introduced in this manuscript, for the first time. The precursor powder was calcined between 200 °C and 850 °C for 3 h in air. Phase formation, crystalline nature, morphology and chemical purity of the fabricated CCZTO were investigated with TG/DTA, FT-IR, FT-Raman, XRD, SAED patterns, SEM, TEM, EDX and XPS analyses, respectively. The XRD results indicated that all sintered samples had a major CaCu3Ti4O12 structure with some amount of CaTiO3 and CuO. The bright-field TEM micrographs revealed that the particle size was in the range of 15–50 nm, which was in good agreement with the average crystallite size obtained from XRD. SEM micrographs of the sintered CCZTO ceramics showed the average grain sizes were in the range of 800 nm–7 μm. EDX and XPS studies confirmed the stoichiometry and purity of the ceramics. The nature of the relaxation behavior of the ceramics was rationalized using impedance and modulus spectroscopy. The activation energies calculated from the grain-boundary relaxation time constant were found to be in the range of 0.79–0.52 eV, which confirmed the Maxwell–Wagner type of relaxation present in the ceramic. Our inexpensive novel solution chemistry based method for CCZTO_16h gives a high dielectric constant (799) and low dielectric loss (0.091) at 100 Hz at room temperature, which has potential significance for cost-effective technological applications in microelectronic devices.
APL Materials | 2018
Aman Ullah; Hafiza Bushra Gul; Amir Ullah; Muhammad Sheeraz; Jong-Seong Bae; Wook Jo; Chang Won Ahn; Ill Won Kim; Tae Heon Kim
A thermotropic phase boundary between non-ergodic and ergodic relaxor phases is tuned in lead-free Bi1/2Na1/2TiO3-based ceramics through a structural transition driven by compositional modification (usually named as “morphotropic approach”). The substitution of Bi(Ni1/2Ti1/2)O3 for Bi1/2(Na0.78K0.22)1/2TiO3 induces a transition from tetragonal to “metrically” cubic phase and thereby, the ergodic relaxor ferroelectric phase becomes predominant at room temperature. A shift of the transition temperature (denoted as TF-R) in the non-ergodic-to-ergodic phase transition is corroborated via temperature-dependent dielectric permittivity and loss measurements. By monitoring the chemical composition dependence of polarization-electric field and strain-electric field hysteresis loops, it is possible to track the critical concentration of Bi(Ni1/2Ti1/2)O3 where the (1 − x)Bi0.5(Na0.78K0.22)0.5TiO3-xBi(Ni0.5Ti0.5)O3 ceramic undergoes the phase transition around room temperature. At the Bi(Ni0.5Ti0.5)O3 content of x = ...
Ferroelectrics | 2010
Ali Hussain; Chang-Won Ahn; Amir Ullah; Jung Shin Lee; In-Koo Kim
Lead-free piezoelectric Bi0.5(Na0.78K0.22)0.5TiO3–(Na0.5K0.5)NbO3 ceramics have been synthesized by a conventional solid-state reaction methods at different sintering temperatures (1100–1200°C). The effect of sintering temperature on the crystal structure, density and electrical properties was investigated. The Bi0.5(Na0.78K0.22)0.5TiO3–(Na0.5K0.5)NbO3 ceramics sintered at an optimum temperature of 1150°C exhibited high density and electrical properties. High field-induced strain (0.22%) and high dynamic piezoelectric coefficient (S max/E max = d*33 = 440 pm/V) were obtained for samples sintered at 1150°C. These results are believed to be due to the high density and lower conductivities at this temperature.
Journal of The European Ceramic Society | 2014
Amir Ullah; Rizwan Ahmed Malik; Aman Ullah; Dae Su Lee; Soon Jong Jeong; Jae Shin Lee; Ill Won Kim; Chang Won Ahn
Journal of the American Ceramic Society | 2014
Amir Ullah; Aman Ullah; Ill Won Kim; Dae Su Lee; Soon Jong Jeong; Chang Won Ahn
Materials Science in Semiconductor Processing | 2015
Laxman Singh; Ill Won Kim; Byung Cheol Sin; Amir Ullah; Sang Kook Woo; Youngil Lee
Journal of Electroceramics | 2014
Amir Ullah; Chang Won Ahn; Rizwan Ahmed Malik; Jae Shin Lee; Ill Won Kim
Physica B-condensed Matter | 2014
Amir Ullah; Chang Won Ahn; Rizwan Ahmed Malik; Ill Won Kim
Ceramics International | 2014
Amir Ullah; Aman Ullah; Won Seok Woo; Chang Won Ahn; Ill Won Kim