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Jamil Ur Rahman,Ali Hussain,Adnan Maqbool,Rizwan Ahmed Malik,송태권,김명호,이순일,김원정 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.4
Lead-free piezoelectric ceramics (1−x) [(0.97Bi0.5Na0.5TiO3)]-0.03BaZrO3-xLiNbO3 (BNT-BZ3-xLN) with x = (0 − 0.07) were synthesized using the conventional solid-state reaction method, andtheir crystal structure, microstructure, and dielectric, ferroelectric and piezoelectric properties wereinvestigated as a function of the LN content. The X-ray diffraction patterns revealed the formationof a single-phase perovskite structure for all the LN-modified BNT-BZ ceramics in this study. Theresults indicate that the LN substitution into BNT-BZ3 induces a transition from a ferroelectricto a diffuse and/or relaxor state accompanying a field-induced strain of 0.20% for x = 0.05 at anapplied field of 6 kV/mm. The corresponding dynamic piezoelectric coefficient for this compositionwas (Smax/Emax = 333 pm/V). A significant reduction of the coercive field (Ec) and enhancementof the piezoelectric constant (d33) from 98 pC/N for x = 0 to 117 pC/N x = 0.01 was observed.
Jamil Ur Rahman,Ali Hussain,Adnan Maqbool,Rizwan Ahmed Malik,송태권,김명호,이순일,김원정 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.7
Lead-free piezoelectric 0.97(Bi0.5Na0.5Ti1−xNbx)O3-0.03BaZrO3 (BNT-BZ3) ceramics (x = 0 0.03) were prepared by a conventional solid-state reaction method. X-ray diffraction patterns revealed the formation of single-phase perovskite structure with x 0.015. The depolarization temperature and the dielectric constant decreased with increasing Nb content. The remanent polarization (Pr) and the piezoelectric constant (d33) increased from 28 μC/cm2 and 98 pC/N for x = 0 to 31 μC/cm2 and 128 pC/N for x = 0.005, respectively. In addition, the electric field induced strain was enhanced with a maximum value Smax = 0.17% with a normalized piezoelectric coefficient of d 33 = 283 pm/V at an applied electric field of 6 kV/mm for x = 0.015.
Jamil Ur Rahman,Ali Hussain,Adnan Maqbool,Rizwan Ahmed Malik,김민수,김명호 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.7
In this work, lead-free 0.945B0.5N0.5TiO3-0.055BaZrO3 (BNT-BZ) ceramics were synthesized byusing conventional solid-state reaction method and the effect of different sintering temperatures(1145 − 1200◦C) on its structure and electromechanical properties were investigated. XRD patternsrevealed single a phase-perovskite structure for all samples sintered at different temperatures. An optimum sintering temperature enhanced densification, promoted grain growth, and improvethe dielectric and piezoelectric properties. However, at low (1145◦C) and high (1200◦C) sinteringtemperatures, the BNT-BZ ceramics showed inferior electromechanical properties. BNT-BZ ceramicssintered at an optimum temperature (1175◦C) showed an enhanced strain (0.39%) responseat an applied electric field of 7 kV/mm with a high dynamic piezoelectric coefficient (d∗33 = 557pm/V). These results can be attributed to the high density of the BNT-BZ ceramics sintered at1175◦C.
Grain 크기 조절을 통한 n-Type Bi2Te3 열전 소재 특성 향상
이나영,예성욱,Rahman Jamil Ur,탁장렬,조중영,서원선,신원호,남우현,노종욱 한국마이크로전자및패키징학회 2021 마이크로전자 및 패키징학회지 Vol.28 No.4
The enhancement of thermoelectric figure of merit was achieved by the simple processes of sieving and high energy ball milling, respectively, which are enable to reduce the grain size of n-type Bi2Te3 thermoelectric materials. By optimizing the grain size, the electrical conductivities and thermal conductivities were controlled. In this study, spark plasma sintering was employed for hindering the grain growth during the sintering process. The thermoelectric figure of merit was measured to be 0.78 in the samples with 30 min high energy ball milling process. Notably, this value was 40 % higher than that of pristine Bi2Te3 sample. This result shows the properties of thermoelectric materials can be readily controlled by optimization of grain size via simple ball milling process. 본 연구에서는 체가름과 고에너지 볼 밀링 공정이 n-type Bi2Te3 열전 재료의 전기적 및 열적 수송 특성에 미치는 영향을 검토하였다. 입자 크기가 감소한 분말의 특성을 유지하기 위하여 짧은 시간 안에 소결이 가능한 방전 플라즈마 소결 공정 (spark plasma sintering, SPS)을 진행하였다. 그 결과, 밀링 처리를 진행한 소결체의 열전 성능지수가 향상되었으며, 30분동안 고에너지 볼 밀링 공정을 거친 샘플이 425 K에서 0.78의 최대 열전 성능지수를 가지는 것을 확인하였다. 이는 손쉬운 공정을 이용하여 결정립 크기 감소를 통한 phonon의 격자 산란을 효과적으로 유도한 결과이다. 동시에 n-type Bi2Te3에서 anti-site defect와 같은 결함을 제어함으로써 캐리어 농도를 증가시킬 수 있음을 본 연구를 통하여 확인하였다.
매트랩/시뮬링크 simulation model을 이용한 열전 모듈의 효율 예측
이나영,예성욱,Rahman Jamil Ur,탁장렬,조중영,서원선,신원호,Walter Commerell,남우현,노종욱 대한금속·재료학회 2021 대한금속·재료학회지 Vol.59 No.11
Development new high-performance thermoelectric materials for more efficient power generation systems and eco-friendly refrigerating systems has been challenging. Over the past few decades, thermoelectric studies have been focused on increasing the thermoelectric properties of materials. However, for conventional applications, developing of thermoelectric devices or modules with lower cost and simpler fabrication processes is also important. Simulation models that can predict the thermoelectric efficiency of modules using the thermoelectric properties of materials are needed for this purpose. In this study, we developed a simple model for calculating the efficiency of thermoelectric modules using MATLAB/Simulink. In this model, the temperature difference between the hot source and heat sink was fixed to ensure the precise comparisons of thermoelectric efficiency. The electric resistivity and Seebeck coefficient of thermoelectric materials was used in order to predict the efficiency of the thermoelectric modules. Then, the efficiency of the thermoelectric modules was verified using measured values which had been reported in prior experimental works. In this study, the simulated values were higher than the real thermoelectric effiency values. To address this, the simulations should consider the thermal resistance or electric contact resistance between the thermoelectric materials and electrodes.
Hussain, Ali,Rahman, Jamil Ur,Ahmed, Faheem,Kim, Jin-Soo,Kim, Myong-Ho,Song, Tae-Kwon,Kim, Won-Jeong Elsevier 2015 Journal of the European Ceramic Society Vol.35 No.3
<P><B>Abstract</B></P> <P>In this work, plate-like Na<SUB>0.5</SUB>Bi<SUB>0.5</SUB>TiO<SUB>3</SUB> (NBT) particles were successfully synthesized from a bismuth layer-structured ferroelectric Na<SUB>0.5</SUB>Bi<SUB>4.5</SUB>Ti<SUB>4</SUB>O<SUB>15</SUB> (NBT4) precursor by a topochemical microcrystal conversion (TMC) method. Because of the high anisotropic structure, plate-like NBT4 particles were first synthesized by molten salt process. After topochemical reaction with the complementary reactants (Na<SUB>2</SUB>CO<SUB>3</SUB>) and TiO<SUB>2</SUB> at 950°C for 4h in NaCl flux, the layer structure of the NBT4 particles was transformed into a simple perovskite NBT template. The resulting large NBT templates had plate-like shape, an average size of 10–15μm and retained the morphological features of the NBT4 precursor. The large as synthesized plate-like NBT particles were utilized to fabricate textured 99.40 Na<SUB>0.5</SUB>Bi<SUB>0.5</SUB>TiO<SUB>3</SUB>-0.60BaZrO<SUB>3</SUB> (NBT-BZ) ceramics via the templated grain growth (TGG) method.</P>
Adnan Maqbool,Ali Hussain,Jamil Ur Rahman,Rizwan Ahmed Malik,송태권,Myong Ho Kim,Won Jeong Kim 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.12
The influence of SrZrO3 (SZ) addition on the crystal structure, piezoelectric and the dielectric properties of lead-free Bi0.5Na0.5TiO3 (BNT−SZ100x, with x = 0 − 0.10) ceramics was systematically investigated. A significant reduction in the grain size was observed with SZ substitution. The X-ray diffraction analysis of the sintered BNT−SZ ceramics revealed a single perovskite phase with a pseudocubic symmetry; however, electric poling indicated a non-cubic distortion in the poled BNT−SZ ceramics. With increase in the SZ content, the temperature of maximum dielectric constant (Tm) shifted towards lower temperatures, and the curves became more diffuse. Enhanced piezoelectric constant (d33 = 102 pC/N) and polarization response were observed for the BNT−SZ5 ceramics. The results indicated that SZ substitution induced a transition from a ferroelectric to relaxor state with a field-induced strain of 0.24% for BNT−SZ9 corresponding to a normalized strain of 340 pm/V.