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Akram, Fazli,Ahmed Malik, Rizwan,Hussain, Ali,Song, Tae-Kwon,Kim, Won-Jeong,Kim, Myong-Ho Elsevier 2018 Materials letters Vol.217 No.-
<P><B>Abstract</B></P> <P>LiTaO<SUB>3</SUB> (LT)-modified (1 − <I>x</I>)(0.675BiFeO<SUB>3</SUB>–0.325BaTiO<SUB>3</SUB>) + 0.6 mol% MnO<SUB>2</SUB> + 0.4 mol% CuO (BFBTMC–<I>x</I>LT, where <I>x</I> = 0–0.030) ceramics were synthesized by solid state reaction method. The crystal symmetry, ferroelectric response, and temperature stable dielectric properties were investigated as a function of different LT-content. The X-ray diffraction study of BFBTMC–LT piezoceramics revealed no remarkable variation in the crystal symmetry. The value of maximum polarization (<I>P</I> <SUB>m</SUB> ≈ 24 μC/cm<SUP>2</SUP>) and remnant polarization (<I>P</I> <SUB>r</SUB> ≈ 18 μC/cm<SUP>2</SUP>) were obtained at BFBTMC–0.010LT composition. The maximum temperature of permittivity (<I>T</I> <SUB>max</SUB>) decreased by the addition of LT-content in BFBTMC materials. The un-doped sample was ferroelectric; a change to relaxor behavior occurred by the addition of LT-content, with broad frequency dependent curves of dielectric mid-value permittivity (ε<SUB>rmid</SUB>) and tangent loss as a function of temperature. A significant enhancement occurred at 3 mol% LT-modified BFBTMC ceramics, with ε<SUB>rmid</SUB> = 5000 ± 9.5% (250–450 °C at 1 kHz). These results are favorable for practical applications in high temperature dielectrics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> LiTaO<SUB>3</SUB>-modified BiFeO<SUB>3</SUB>–BaTiO<SUB>3</SUB> dielectric ceramics were prepared. </LI> <LI> Easy and reproducible solid state reaction method was used. </LI> <LI> Temperature stable dielectric of 5000 ± 9.5% was achieved in the range 250–450 °C. </LI> </UL> </P>
Akram, Fazli,Malik, Rizwan Ahmed,Song, Tae Kwon,Lee, Soonil,Kim, Myong-Ho Elsevier 2019 Journal of the European Ceramic Society Vol.39 No.7
<P><B>Abstract</B></P> <P>The thermal stability of the dielectric behavior and the crystal structure, surface morphology, polarization, and piezoelectric properties of lead-free BiGaO<SUB>3</SUB> (BG)-modified 0.65Bi<SUB>1.05</SUB>FeO<SUB>3</SUB>–0.35BaTiO<SUB>3</SUB> (abbreviated as BF–BT–<I>x</I>BG with 0 ≤ <I>x</I> ≤ 0.03) ceramics were investigated. XRD analysis of BF–BT–<I>x</I>BG dielectric ceramics revealed no remarkable change in the crystal structure within the studied composition range. Around the critical composition (BF–BT–0.02BG), the piezoelectric constant (<I>d</I> <SUB>33</SUB>) and electromechanical coupling factor (<I>k</I> <SUB>p</SUB>) reached maximum values of ⁓205 pC/N and 34.5%, respectively. The BF–BT–BG dielectric system also exhibited a thermally-stable ε<SUB>r</SUB> (801–902, at 30 °C – 500 °C), high <I>T</I> <SUB>max</SUB> (395 °C – 416 °C), colossal ε<SUB>rmax</SUB> (46,363–76,303), and ε<SUB>rmid</SUB> (2241 ± 15%–3678 ± 15%, with tan<I>δ</I> ≤ 0.08) across a wide temperature range of 198 °C–332 °C. This improvement in the dielectric properties and high <I>T</I> <SUB>max</SUB> of the optimum specimen can be attributed to the BiGaO<SUB>3</SUB>-modification and quenching process, which made the system viable for applications that require high-temperature dielectric stability.</P>
Akram, Fazli,Malik, Rizwan Ahmed,Lee, Soonil,Pasha, Riffat Asim,Kim, Myong Ho Materials Research Society of Korea 2018 한국재료학회지 Vol.28 No.9
Lead free $(1-x)(0.675BiFeO_3-0.325BaTiO_3)-xLiTaO_3$ (BFBTLT, x = 0, 0.01, 0.02, and 0.03, with 0.6 mol% $MnO_2$ and 0.4 mol% CuO) were prepared by a solid state reaction method, followed by air quenching and their crystalline phase, morphology, dielectric, ferroelectric and piezoelectric properties were explored. An X-ray diffraction study indicates that lithium (Li) and tantalum (Ta) were fully incorporated in the BFBT materials with the absence of any secondary phases. Dense ceramic samples (> 92 %) with a wide range of grain sizes from $3.70{\mu}m$ to $1.82{\mu}m$ were obtained in the selected compositions ($0{\leq}x{\leq}0.03$) of BFBTLT system. The maximum temperatures ($T_{max}$) were mostly higher than $420^{\circ}C$ in the studied composition range. The maximum values of maximum polarization ($P_{max}{\approx}31.01{\mu}C/cm^2$), remnant polarization ($P_{rem}{\approx}22.82{\mu}C/cm^2$) and static piezoelectric constant ($d_{33}{\approx}145pC/N$) were obtained at BFBT-0.01LT composition with 0.6 mol% $MnO_2$ and 0.4 mol% CuO. This study demonstrates that the high $T_{max}$ and $d_{33}$ for BFBTLT ceramics are favorable for industrial applications.
Electromechanical properties of ternary BiFeO3−0.35BaTiO3-BiGaO3 piezoelectric ceramics
Akram, Fazli,Malik, Rizwan Ahmed,Khan, Salman Ali,Hussain, Ali,Lee, Soonil,Lee, Myang-Hwan,In, Choi Hai,Song, Tae-Kwon,Kim, Won-Jeong,Sung, Yeon Soo,Kim, Myong-Ho Springer-Verlag 2018 JOURNAL OF ELECTROCERAMICS Vol.41 No.1
Salman Ali Khan,Tauseef Ahmed,Fazli Akram,Jihee Bae,Soo Yong Choi,Tran Thi Thanh,Mingyu Kim,송태권,성연수,Myong‑Ho Kim,Soonil Lee 한국세라믹학회 2020 한국세라믹학회지 Vol.57 No.3
In this study, 0.65Bi1.05FeO3–0.35BaTiO3 (BF-35BT) lead-free piezoelectric ceramics were prepared using a conventional solid-state method to determine the effects of sintering temperature on their microstructures and electrical properties. The average grain size increased with sintering temperature, but not significantly, and the relative density of the ceramics increased and then decreased at high sintering temperatures due to the volatilization of Bi2O3. At the optimal sintering temperature (1030 °C), BF-35BT ceramics showed minimum coercive field (Ec) with enhanced remanent polarization (Pr) and consequently resulted in a high converse piezoelectric coefficient (d* 33) value of 305 pm/V. The results indicate that the optimum sintering temperature, maximum relative density, and appropriate grain size, which are significantly related to the domain size and configuration, as well as the minimum concentration of associated charged defects, are critical factors that influence the piezoelectric performance of BF-35BT ceramics.
Synthesis of Ni-based fluoroperovskites by solvent-free mechanochemical reaction
Choi Jin San,Sheeraz Muhammad,Akram Fazli,Han Hyoung-Su,Lee Jae-Shin,Ahn Chang Won,Kim Tae Heon 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.11
We realized fluoride perovskites ANiF3 (A = Na, K, and Ag) incorporating a transition-metal Ni element using solvent-free mechanochemical reaction processes. Methodologically, two different synthetic routes were devised based on the conventional mechanical grinding and the planetary ball milling techniques. The structural characteristics of the as-synthesized fluoroperovskite powders were determined by powder X-ray diffraction measurements and subsequent Rietveld refinement analyses. The band gaps and the chemical compositions of the ANiF3 powders were also examined by ultraviolet–visible absorption measurements and element-specific energy dispersive X-ray spectroscopy, respectively. The goodness of factors of our refinements revealed that the high-energy planetary ball milling was more beneficial than the conventional grinding method in achieving a perovskite ANiF3 phase mechanically. We found that the degree of mechanochemical reaction to form the perovskite phase depended on the crystal structure. With the fitted lattice parameters of the fluoride perovskites, we discussed how a structural modification induced by cation non-stoichiometry affected the stabilization of the fluoroperovskite materials via the mechanochemical synthesis.
Kumar Akshay,Vij Ankush,Huh Seok Hwan,Kim Jong-Woo,Sharma Mohit K.,Kumari Kavita,Yadav Naveen,Akram Fazli,구본흔 한국물리학회 2023 Current Applied Physics Vol.49 No.-
We investigated the influence of structural disorders on the magnetic and magnetocaloric (MC) properties upon A-site rare-earth substitution in A1.4Sr1.6Mn2O7 (A = La, Pr, Nd) Ruddlesden-Popper (R–P) compounds. The samples were produced through the solid-state method, and the structural analysis indicated formation of R–P phase with the Jahn-Teller distortion parameter varying from highest in La1.4Sr1.6Mn2O7 (LSMO) to Nd1.4Sr1.6Mn2O7 (NSMO) and followed by Pr1.4Sr1.6Mn2O7 (PSMO). Hence, the magnetization value was increased in LSMO sample implying an enhanced interbilayer and interlayer spin correlations. It resulted in a high value of MC parameters like temperature average entropy change (TEC) and relative cooling power (RCP) of 4.21 J/kgK and 87 J/kg for LSMO, while lowest value of 0.53 J/kgK and 27 J/kg for PSMO respectively, at 2.5 T field. The room temperature MC response in PSMO, whereas a large TEC in LSMO and NSMO compounds advocate their candidacy in broad range of refrigeration applications.