Hydrothermal method for the synthesis of sb2te3, and bi0.5sb1.5te3 nanoplates and their thermoelectric properties

Dharmaiah, Peyala,Hong, Soon‐,Jik Wiley-Blackwell 2018 International journal of applied ceramic technolog Vol.15 No.1

Luminescence and energy transfer in Dy³⁺/Tb³⁺ co-doped transparent oxyfluorosilicate glass-ceramics for green emitting applications

Dharmaiah, P.,Viswanath, C.S.D.,Basavapoornima, Ch.,Krishnaiah, K.V.,Jayasankar, C.K.,Hong, S.J. Pergamon Press 2016 Materials research bulletin Vol.83 No.-

Transparent oxyfluorosilicate glass-ceramics containing cubic SrF<SUB>2</SUB> nanocrystals doped with Dy<SUP>3+</SUP>, Tb<SUP>3+</SUP>, and Dy<SUP>3+</SUP>/Tb<SUP>3+</SUP> were successfully synthesized by melt quenching followed by heat treatment process. The crystalline phase of SrF<SUB>2</SUB> nanocrystals during heat treatment was confirmed by X-ray diffraction. The emission intensity of glass-ceramics is much stronger than that of their parent glasses, on the one hand due to progressive incorporation of Dy<SUP>3+</SUP> and Tb<SUP>3+</SUP> ions within the SrF<SUB>2</SUB> nanocrystals, on the other hand due to an efficient energy transfer from Dy<SUP>3+</SUP> to Tb<SUP>3+</SUP>. Luminescence quantum efficiency of the samples was measured by using an integrating sphere. Luminescence decay curves of the <SUP>4</SUP>F<SUB>9/2</SUB> level were fitted to Inokuti-Hirayama (IH) model for analyzing the energy transfer rates between Dy<SUP>3+</SUP> and Tb<SUP>3+</SUP> ions. The chromaticity coordinates were determined from the measured emission spectra and they are located at the green and white light regions.

Thermoelectric Properties of Bi2Te3 Nanocrystals with Diverse Morphologies Obtained via Modified Hydrothermal Method

Dharmaiah, P.,Hong, S. J. Springer Science + Business Media 2017 Journal of electronic materials Vol.46 No.5

<P>Single-phase Bi2Te3 nanostructures (spherical and flower-like) have been synthesized using a modified hydrothermal method at different reaction temperatures (70A degrees C, 100A degrees C, and 150A degrees C) and subsequently consolidated by spark plasma sintering. Their crystal structure, morphology, and thermoelectric and mechanical properties were investigated. The results suggest that the reaction temperature had a significant effect on the morphology and thermoelectric properties. The presence of nanostructures in bulk samples led to a remarkable decrease in thermal conductivity with a lesser effect on electrical conductivity. As a result, the figurea of pound merit (ZT) of the spark-plasma-sintered sample processed from spherical nanoparticles reached 0.54 at 400 K. The Vickers microhardness of the bulk sample processed from spherical nanoparticles was higher than the best results found in literature.</P>

Formation mechanism of twin structures in <i>p-type</i> (Bi_0.25Sb_0.75)₂Te₃ thermoelectric compound

Lee, Kap Ho,Dharmaiah, Peyala,Hong, Soon-Jik Elsevier 2019 Scripta materialia Vol.162 No.-

<P><B>Abstract</B></P> <P>The formation mechanism of twin structures in <I>p-type</I> (Bi<SUB>0.25</SUB>Sb<SUB>0.75</SUB>)<SUB>2</SUB>Te<SUB>3</SUB> compound was examined using high-resolution transmission electron microscopy (HR-TEM) and computer simulations. The results shown that the formation of twins is analogous to the twinning mechanism via synchronized activation of Shockley partial dislocations commonly observed terminating {111} growth and annealing twins in face centered cubic (FCC) metals. The 10 1 ¯ 0 boundary, as an incoherent twin boundary (ITB), is mobile due to its lower shear stress compared to that of the coherent {0001} twin boundary; thickness of the twin region can be reduced or increased according to the direction of the movement.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of Acid Dissolution Conditions on Recovery of Valuable Metals from Used Plasma Display Panel Scrap

Kim, Chan-Mi,Dharmaiah, Peyala,Kim, Hyo-Seob,Koo, Jar-Myung,Yoon, Jae-Sik,Hong, Hyun-Seon,Hong, Soon-Jik PAS 2017 ARCHIVES OF METALLURGY Vol.62 No.2

<P>The objective of this particular study was to recover valuable metals from waste plasma display panels using high energy ball milling with subsequent acid dissolution. Dissolution of milled (PDP) powder was studied in HCl, HNO3, and H2SO4 acidic solutions. The effects of dissolution acid, temperature, time, and PDP scrap powder to acid ratio on the leaching process were investigated and the most favorable conditions were found: (1) valuable metals (In, Ag, Mg) were recovered from PDP powder in a mixture of concentrated hydrochloric acid (HCl: H2O = 50:50); (2) the optimal dissolution temperature and time for the valuable metals were found to be 60 degrees C and 30 min, respectively; (3) the ideal PDP scrap powder to acid solution ratio was found to be 1:10. The proposed method was applied to the recovery of magnesium, silver, and indium with satisfactory results.</P>

Enhanced thermoelectric properties of Bi_0.5Sb_1.5Te₃ composites with in-situ formed senarmontite Sb₂O₃ nanophase

Kim, Eun Bin,Dharmaiah, Peyala,Lee, Kap-Ho,Lee, Chul-Hee,Lee, Jong-Hyeon,Yang, Jae-Kyo,Jang, Dae-Hwan,Kim, Dong-Soo,Hong, Soon-Jik Elsevier 2019 Journal of alloys and compounds Vol.777 No.-

<P><B>Abstract</B></P> <P>A lot of efforts being invested into producing efficient thermoelectric devices based on Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> materials for room temperature applications. Key research achievements of these efforts that incorporation of oxide nanoparticles into Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> materials exhibit higher thermoelectric performance in nano-composite form. Here, we prepared Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> nanocomposite incorporated with TeO<SUB>2</SUB> nanoparticles (NPs) by high energy ball milling and spark plasma sintering, where <I>in-situ</I> Sb<SUB>2</SUB>O<SUB>3</SUB> phase and triple functional interfaces were developed. The formation mechanism of <I>in-situ</I> Sb<SUB>2</SUB>O<SUB>3</SUB> phase in the Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB>/TeO<SUB>2</SUB> composites was explored by the thermodynamic calculations; microstructural features and material composition in the bulk samples were investigated using high-resolution transmission electron microscopy (HRTEM) coupled with energy dispersive X-ray spectroscopy (EDS). The formation of interfaces between <I>in situ</I> senarmontite Sb<SUB>2</SUB>O<SUB>3</SUB> nanophase and Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> matrix causes an enhanced Seebeck coefficient by ∼20% due to increase of carrier energy filtering and significant reduction of thermal conductivity by ∼77% ascribed to intensified phonon scattering or trapping at 350 K. As a result, an improved dimensionless figure of merit (ZT) of 1.07 at 350 K was achieved in a Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB>/3 wt%TeO<SUB>2</SUB> composites. The proposed <I>in-situ</I> reaction and interface formation mechanisms are expected to open the possibility of further increases in ZT.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Formation of <I>in-situ</I> Sb<SUB>2</SUB>O<SUB>3</SUB> phase in the Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB>/TeO<SUB>2</SUB> composites was explored. </LI> <LI> Sb<SUB>2</SUB>O<SUB>3</SUB> phase is obtained by <I>in-situ</I> reaction of Sb with TeO<SUB>2</SUB> during milling and SPS. </LI> <LI> The Seebeck coefficient was enhanced owing to increase of energy filtering effect. </LI> <LI> Thermal conductivity was reduced (77%) due to phonon scattering at interfaces. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Investigation of microstructure and thermoelectric properties at different positions of large diameter pellets of Bi_0.5Sb_1.5Te₃ compound

Park, Ki-Chan,Dharmaiah, Peyala,Kim, Hyo-Seob,Hong, Soon-Jik Elsevier 2017 Journal of alloys and compounds Vol.692 No.-

<P><B>Abstract</B></P> <P>The conversion efficiency of typical thermoelectric materials is still below 10% which leads the cost of the device was high. Recently, considerable attention has been paid to reduce the production cost and reliability of the performance. In this work, a low cost and an efficient method for large-scale production of high-quality thermoelectric powders via high-pressure gas atomization process and it have been sintered to a large diameter of pellets (50 mm) by spark plasma sintering process. The current and power densities of large diameter SPS processed specimens varied from center to edge portion. In order to verify the reliability of large diameter pellets, we investigated microstructure, thermoelectric and mechanical properties at different positions of pellets. The grain size variations could be clearly identified using SEM and EBSD techniques from center to edge part of pellets. Enhanced Seebeck coefficient and reduction of thermal conductivity for edge part of pellet were due to microstructure refinement which mainly occurs from temperature gradient during the sintering process. As a result, mechanical and thermoelectric properties were significantly enhanced. Ultimately, the thermoelectric performance of the large diameter pellets exhibits almost nearly equal from center to the edge which reaches 1.25 at 348 K.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Thermoelectric powders were fabricated using cost effective gas-atomization process. </LI> <LI> Investigated thermoelectric properties at different positions of 50Φ diameter pellet. </LI> <LI> The grain size variations could clearly identified at different position of pellet. </LI> <LI> The ZT of large diameter pellets exhibits almost nearly equal from center to the edge. </LI> <LI> The highest ZT of 1.25 at 348 K was achieved for center position of the pellet. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Oxide formation mechanism and its effect on the microstructure and thermoelectric properties of <i>p-type</i> Bi_0.5Sb_1.5Te₃ alloys

Lwin, May Likha,Dharmaiah, Peyala,Madavali, Babu,Lee, Chul-Hee,Shin, Dong-won,Song, Gian,Lee, Kap-Ho,Hong, Soon-Jik Elsevier 2018 Intermetallics Vol.103 No.-

<P><B>Abstract</B></P> <P>Bismuth antimony telluride based thermoelectric (TE) materials have been intensively developed and synthesized using different mechanisms, for the room temperature TE applications. In particular, bismuth antimony telluride based TE alloys are very sensitive to deviations in their composition, and to contamination during the materials synthesis. Oxygen contamination during Bi-Sb-Te based materials synthesis is one of the critical factors that alters or diminishes thermoelectric-transport properties. Thus, in this study, how the oxide formation mechanism on the powder surface and bulks of p-type Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> alloys affected the microstructural features and thermoelectric properties were elucidated quantitatively. While applying heat treatment (HT) to Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> powder, the constituent elements interacted with the ambient atmosphere and formed a new oxide phase which acted as a barrier to carrier transport. At the initial stage (300 °C) of heat treatment, only the powder surface was oxidized due to the reaction of outer surface atoms with atmospheric air and moisture. While increasing in temperature during HT, this surface oxygen contamination diffused further inside the powder through the grain boundaries. More diffusion and spreading occurred throughout the matrix at 450 °C. The increment of oxygen content from 0.05 to 0.82 wt% drastically decreased the electrical conductivity by 67%, and thermal conductivity by 7% at the heat treatment temperature of 450 °C. This reduction behavior is mainly due to severe scattering of the carriers/phonons at the new formation of oxide (Sb<SUB>2</SUB>O<SUB>3</SUB>) phase near grain boundaries and within the matrix. At a glance, a small increase in the oxygen content wouldn't significantly influence the thermoelectric properties; however, at a certain level of oxide formation (0.82 wt%), severe effects could occur due to the intensified scattering or trapping of carriers by the oxide barrier formation at the grain boundaries.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Determined the oxygen concentration of different heat-treated GA powder and SPS bulks. </LI> <LI> Elucidation the relation between the mechanism of oxide formation and the thermoelectric properties of Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> alloys. </LI> <LI> Identified Sb<SUB>2</SUB>O<SUB>3</SUB> phase at the grain boundary and within the grains. </LI> <LI> Demonstrated the thermoelectric performance in Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> alloys with oxygen content. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Large-scale production of (GeTe)_<i>x</i>(AgSbTe₂)_{100−<i>x</i>} (x=75, 80, 85, 90) with enhanced thermoelectric properties via gas-atomization and spark plasma sintering

Kim, Hyo-Seob,Dharmaiah, Peyala,Madavali, Babu,Ott, Ryan,Lee, Kap-Ho,Hong, Soon-Jik Elsevier 2017 ACTA MATERIALIA Vol.128 No.-

<P>(GeTe)(x)(AgSbTe2)(100-x): TAGS thermoelectrics are an attractive class of materials due to their combination of non-toxicity and good conversion efficiency at mid-temperature ranges. In the present work, we have utilized energy and time efficient high-pressure gas atomization and spark-plasma sintering techniques for large-scale preparation of samples with varying composition (i.e., (GeTe)(x)(AgSbTe2)(100-x) where x = 75, 80, 85, and 90). High-temperature x-ray diffraction was used to understand the phase transformation mechanism of the as-atomized powders. Detailed high-resolution transmission electron microscopy of the sintered samples revealed the presence of nanoscale precipitates, antiphase, and twin boundaries. The nanoscale twins and antiphase boundaries serve as phonon scattering centers, leading to the reduction of total thermal conductivity in TAGS-80 and 90 samples. The maximum ZT obtained was 1.56 at 623 K for TAGS-90, which was similar to 94% improvement compared to values previously reported. The presence of the twin boundaries also resulted in a high fracture toughness (K-IC) of the TAGS-90 sample due to inhibition of dislocation movement at the twin boundary. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.</P>

Investigation of Thermoelectric Properties with Dispersion of Fe2O3 and Fe-85Ni Nanospheres in Bi0.5Sb1.5Te3 Matrix

Yoon, S. M.,Dharmaiah, P.,Kim, H. S.,Lee, C. H.,Hong, S. J.,Koo, J. M. Springer Science + Business Media 2017 Journal of electronic materials Vol.46 No.5

<P>In this work, we fabricated Bi0.5Sb1.5Te3 thermoelectric alloys using the mass-production technique, and subsequently Fe2O3 and Fe-85Ni alloy nanoparticles were dispersed in the matrix by high energy ball milling and consolidated using spark plasma sintering technique. The influence of Fe2O3 and Fe-85Ni alloy spherical nanoparticles in Bi0.5Sb1.5Te3 (BST) matrix on thermoelectric transport properties has been investigated. The x-ray diffraction and scanning electron microscopy results show that the nanoparticles were dispersed in the matrix. The spark plasma sintered bulk BST/Fe2O3 composite sample exhibited high Seebeck coefficient which was 39% higher than the bare BST due to low carrier concentration and a significant reduction in the thermal conductivity (38%) owing to enhanced carrier scattering by the dispersed nanoparticles compared to that of the bare BST sample. As a result, the maximum ZT values for the BST, BST/Fe2O3, and BST/Fe-85Ni samples were found as 1.17, 0.98, and 0.88 at 375 K, respectively. Micro Vickers hardness of BST/Fe2O3 and BST/Fe-85Ni composite samples was significantly enhanced compared to bare Bi0.5Sb1.5Te3 sample.</P>