Metal Chalcogenides: A Rich Source of Nonlinear Optical Materials

Chung, In,Kanatzidis, Mercouri G. American Chemical Society 2014 Chemistry of materials Vol.26 No.1

<P>Materials chemistry and the pursuit of new compounds through exploratory synthesis are having a strong impact in many technological fields. The field of nonlinear optics is directly impacted by the availability of enabling materials with high performance. Nonlinear optical (NLO) phenomena such as second harmonic and difference frequency generation (SHG and DFG, respectively) are effective at producing a coherent laser beam in difficult to reach frequency regions of the electromagnetic spectrum. Such regions include the infrared (IR), far-infrared, and terahertz frequencies. High performance NLO crystals are critical for applications utilizing these coherent light sources, and new materials are continuously sought for better conversion efficiency and performance. The class of metal chalcogenides is the most promising source of potential NLO materials with desirable properties particularly in the IR region where most classes of materials face various fundamental challenges. We review the recent developments in the discovery of several new high-performing chalcogenide NLO materials for the IR region of the spectrum. Among these, KPSe<SUB>6</SUB>, NaAsSe<SUB>2</SUB>, and Na<SUB>2</SUB>Ge<SUB>2</SUB>Se<SUB>5</SUB> have been shown to exhibit some of the highest SHG coefficients (χ<SUP>(2)</SUP>) reported, namely, 150, 325, and 290 pm/V, respectively. We focus on their structural characteristics, optical transparency, and nonlinear optical properties. We also discuss a new concept to prepare strong NLO bulk glasses, fibers, and thin films without poling, which would be a promising solution to a main challenge in NLO applications. The impact of cutting-edge theoretical calculations in helping to move this field of materials science and chemistry forward is highlighted.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2014/cmatex.2014.26.issue-1/cm401737s/production/images/medium/cm-2013-01737s_0025.gif'></P>

Analysis of Nanoprecipitates in a Na-Doped PbTe–SrTe Thermoelectric Material with a High Figure of Merit

Kim, Yoon-Jun,Zhao, Li-Dong,Kanatzidis, Mercouri G.,Seidman, David N. American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.26

<P>The dimensionless figure of merit, ZT, of bulk thermoelectric materials depends mainly on the transport properties of charge carriers and heat-carrying phonons. PbTe-4 mol % SrTe doped with 2 mol % Na (Pbw(0.94)Na(0.02)Sr(0.04)Te) is a nanostructured material system that exhibits a ZT higher than 2. The precipitate size distribution of SrTe precipitates is believed to play a key role. This raises the question of whether its performance is limited by precipitate coarsening (Ostwald ripening) at elevated temperatures. Herein, we utilize an atom-probe tomography (APT) to study the number density and mean radii of precipitates in concert with partial radial distribution functions (RDFs) of individual atoms. We find that the SrTe precipitates actually contain oxygen: SrTe1-xOx. We correlate this information with the overall ZT performance, specifically focusing on the electrical and lattice thermal conductivities after isothermal, heat treatments at 300 and 400 degrees C for 7 days, followed by furnace cooling. Comparison of the samples annealed at 400 and 300 degrees C demonstrates significant coarsening of SrTe1-xOx precipitates as well as strong segregation of oxygen impurities in the SiTe1-xOx precipitates. Additionally, on the basis of the partial RDFs, the Na dopant atoms cluster with other Na atoms as well as with Pb, Te, and St atoms; clustering depends strongly on the annealing temperature and concomitantly affects the overall ZT values. We found that the coarsening slightly increases the lattice thermal conductivity and also increases the electrical conductivity, thereby having little or even a beneficial effect on the ZT values. Importantly, these findings demonstrate that APT enables quantitative analyses in three dimensions of the PbTe-4 mol %. SrTe samples in addition to correlation of their properties with the thermoelectric performance.</P>

Low-Temperature Solution-Processed Amorphous Indium Tin Oxide Field-Effect Transistors

Kim, Hyun Sung,Kim, Myung-Gil,Ha, Young-Geun,Kanatzidis, Mercouri G.,Marks, Tobin J.,Facchetti, Antonio American Chemical Society 2009 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.131 No.31

<P>Amorphous indium tin oxide (ITO)-based thin-film transistors (TFTs) were fabricated on various dielectrics [SiO(2) and self-assembled nanodielectrics (SANDs)] by spin-coating an ITO film precursor solution consisting of InCl(3) and SnCl(4) as the sources of In(3+) and Sn(4+), respectively, methoxyethanol (solvent), and ethanolamine (base). These films can be annealed at temperatures T(a) < or = 250 degrees C and afford devices with excellent electrical characteristics. The optimized [In(3+)]/[In(3+) + Sn(4+)] molar ratio (0.7) and annealing temperature (T(a) = 250 degrees C) afford TFTs exhibiting electron mobilities of approximately 2 and approximately 10-20 cm(2) V(-1) s(-1) with SiO(2) and SAND, respectively, as the gate dielectric. Remarkably, ITO TFTs processed at 220 degrees C still exhibit electron mobilities of >0.2 cm(2) V(-1) s(-1), which is encouraging for processing on plastic substrates.</P>

Enhanced thermoelectric properties of p-type nanostructured PbTe–MTe (M = Cd, Hg) materials

Ahn, Kyunghan,Biswas, Kanishka,He, Jiaqing,Chung, In,Dravid, Vinayak,Kanatzidis, Mercouri G. The Royal Society of Chemistry 2013 Energy & environmental science Vol.6 No.5

<P>We investigated the effect of Cd and Hg substitution on the thermoelectric properties of p-type PbTe–<I>x</I>% CdTe and PbTe–<I>x</I>% HgTe (1 ≤<I>x</I>≤ 5) doped with Na<SUB>2</SUB>Te. Both ingot samples and spark plasma sintered (SPS) samples were studied and the properties are compared. We present detailed structural, spectroscopic and transmission electron microscopy (TEM) data, and transport properties of both cast ingot and SPS samples. The SPS processed samples with HgTe as the second phase show better thermoelectric properties than those with CdTe mainly because of more effective phonon scattering. The SPS process gives significantly lower lattice thermal conductivity for the p-type PbTe–HgTe system than the cast ingot. The same effect is not observed in the p-type PbTe–CdTe system. A maximum <I>ZT</I> of ∼1.64 at ∼770 K is achieved for the p-type PbTe–2% HgTe–1% Na<SUB>2</SUB>Te SPS sample. TEM studies reveal the formation of nanostructures whose number density generally increases with increasing concentrations of CdTe and HgTe as the second phase. Meso-scale grain boundaries along with nanostructured precipitates in the SPS samples play an important role in significantly reducing the lattice thermal conductivity compared to cast ingot in the case of p-type PbTe–HgTe.</P> <P>Graphic Abstract</P><P>We investigated the effect of Cd and Hg substitution on the thermoelectric properties of p-type PbTe–<I>x</I>% CdTe and PbTe–<I>x</I>% HgTe (1 ≤<I>x</I>≤ 5) doped with Na<SUB>2</SUB>Te. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3ee40482j'> </P>

Increase in the Figure of Merit by Cd-Substitution in Sn1-xPbxTe and Effect of Pb/Sn Ratio on Thermoelectric Properties

Han, M. K.,Zhou, X.,Uher, C.,Kim, S. J.,Kanatzidis, M. G. Wiley 2012 ADVANCED ENERGY MATERIALS Vol.2 No.10

Semiconducting [(Bi₄Te₄Br₂)(Al₂Cl_6–<i>x</i>Br_<i>x</i>)]Cl₂ and [Bi₂Se₂Br](AlCl₄): Cationic Chalcogenide Frameworks from Lewis Acidic Ioni

Biswas, Kanishka,Chung, In,Song, Jung-Hwan,Malliakas, Christos D.,Freeman, Arthur J.,Kanatzidis, Mercouri G. American Chemical Society 2013 Inorganic chemistry Vol.52 No.10

<P>Lewis acidic organic ionic liquids provide a novel synthetic medium to prepare new semiconducting chalcogenides, [(Bi<SUB>4</SUB>Te<SUB>4</SUB>Br<SUB>2</SUB>)(Al<SUB>2</SUB>Cl<SUB>5.46</SUB>Br<SUB>0.54</SUB>)]Cl<SUB>2</SUB> (<B>1</B>) and [Bi<SUB>2</SUB>Se<SUB>2</SUB>Br](AlCl<SUB>4</SUB>) (<B>2</B>). Compound <B>1</B> features a cationic [(Bi<SUB>4</SUB>Te<SUB>4</SUB>Br<SUB>2</SUB>)(Al<SUB>2</SUB>Cl<SUB>5.46</SUB>Br<SUB>0.54</SUB>)]<SUP>2+</SUP> three-dimensional framework, while compound <B>2</B> consists of cationic layers of [Bi<SUB>2</SUB>Se<SUB>2</SUB>Br]<SUP>2+</SUP>. Spectroscopically measured band gaps of <B>1</B> and <B>2</B> are ∼0.6 and ∼1.2 eV, respectively. Thermoelectric power measurements of single crystals of <B>1</B> indicate an n-type semiconductor.</P><P>Cationic chalcogenide frameworks are rare, but they can be synthesized in organic ionic liquids containing strong Lewis acids such as AlCl<SUB>3</SUB>. The Lewis acidic nature of the medium is believed to favor the assembly of the cationic chalcogenide [Bi<SUB>2</SUB>Q<SUB>2</SUB>Br]<SUP>+</SUP> frameworks.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/inocaj/2013/inocaj.2013.52.issue-10/ic400782c/production/images/medium/ic-2013-00782c_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ic400782c'>ACS Electronic Supporting Info</A></P>

Compression and Aggregation-Resistant Particles of Crumpled Soft Sheets

Luo, Jiayan,Jang, Hee Dong,Sun, Tao,Xiao, Li,He, Zhen,Katsoulidis, Alexandros P.,Kanatzidis, Mercouri G.,Gibson, J. Murray,Huang, Jiaxing American Chemical Society 2011 ACS NANO Vol.5 No.11

<P>Unlike flat sheets, crumpled paper balls have both high free volume and high compressive strength, and can tightly pack without significantly reducing the area of accessible surface. Such properties would be highly desirable for sheet-like materials such as graphene, since they tend to aggregate in solution and restack in the solid state, making their properties highly dependent on the material processing history. Here we report the synthesis of crumpled graphene balls by capillary compression in rapidly evaporating aerosol droplets. The crumpled particles are stabilized by locally folded, π–π stacked ridges as a result of plastic deformation, and do not unfold or collapse during common processing steps. In addition, they are remarkably aggregation-resistant in either solution or solid state, and remain largely intact and redispersible after chemical treatments, wet processing, annealing, and even pelletizing at high pressure. For example, upon compression at 55 MPa, the regular flat graphene sheets turn into nondispersible chunks with drastically reduced surface area by 84%, while the crumpled graphene particles can still maintain 45% of their original surface area and remain readily dispersible in common solvents. Therefore, crumpled particles could help to standardize graphene-based materials by delivering more stable properties such as high surface area and solution processability regardless of material processing history. This should greatly benefit applications using bulk quantities of graphene, such as in energy storage or conversion devices. As a proof of concept, we demonstrate that microbial fuel electrodes modified by the crumpled particles indeed outperform those modified with their flat counterparts.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2011/ancac3.2011.5.issue-11/nn203115u/production/images/medium/nn-2011-03115u_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn203115u'>ACS Electronic Supporting Info</A></P>

Tunneling Electrical Connection to the Interior of Metal–Organic Frameworks

Han, Shuangbing,Warren, Scott C.,Yoon, Seok Min,Malliakas, Christos D.,Hou, Xianliang,Wei, Yanhu,Kanatzidis, Mercouri G.,Grzybowski, Bartosz A. American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.25

<P>Metal–organic frameworks (MOFs) are typically poor electrical conductors, which limits their uses in sensors, fuel cells, batteries, and other applications that require electrically conductive, high surface area materials. Although metal nanoclusters (NCs) are often added to MOFs, the electrical properties of these hybrid materials have not yet been explored. Here, we show that adding NCs to a MOF not only imparts moderate electrical conductivity to an otherwise insulating material but also renders it photoconductive, with conductivity increasing by up to 4 orders of magnitude upon light irradiation. Because charge transport occurs via tunneling between spatially separated NCs that occupy a small percent of the MOF’s volume, the pores remain largely open and accessible. While these phenomena are more pronounced in single-MOF crystals (here, Rb-CD-MOFs), they are also observed in films of smaller MOF crystallites (MIL-53). Additionally, we show that in the photoconductive MOFs, the effective diffusion coefficients of electrons can match the typical values of small molecules diffusing through MOFs; this property can open new vistas for the development of MOF electrodes and, in a wider context, of electroactive and light-harvesting MOFs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-25/jacs.5b03263/production/images/medium/ja-2015-03263s_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5b03263'>ACS Electronic Supporting Info</A></P>

K_4GeP_4Se_12: a case for phase-change nonlinear optical chalcogenide

Jang, J. I.,Park, S.,Harrison, C. M.,Clark, D. J.,Morris, C. D.,Chung, I.,Kanatzidis, M. G. The Optical Society 2013 Optics letters Vol.38 No.8

<P>We report on broadband nonlinear optical (NLO) responses from a phase-change chalcogenide compound K(4)GeP(4)Se(12). Its glassy phase exhibits unusual second-harmonic generation (SHG) due to the preservation of local crystallographic order. The SHG efficiency of the glassy form can be boosted by more than 2 orders of magnitude by simple heat treatment. Strong SHG and third-harmonic generation from both glassy and crystalline compounds were characterized over a wide wavelength range of 1.2-4.0 μm. Our results imply that K(4)GeP(4)Se(12) can be utilized for various NLO applications in the mid-infrared spectrum.</P>

Hybridization Gap in the Semiconducting Compound SrIr₄In₂Ge₄

Calta, Nicholas P.,Im, Jino,Fang, Lei,Chasapis, Thomas C.,Bugaris, Daniel E.,Chung, Duck Young,Kwok, Wai-Kwong,Kanatzidis, Mercouri G. American Chemical Society 2016 Inorganic Chemistry Vol.55 No.23

<P>Large single crystals of SrIr4In2Ge4 were synthesized using the In flux method. This compound is a hybridization gap semiconductor with an experimental optical band gap of E-g = 0.25(3) eV. It crystallizes in the tetragonal EuIr4In2Ge4 structure type with space group I (4) over bar 2m and unit cell parameters a = 6.9004(5) angstrom and c = 8.7120(9) angstrom. The electronic structure is very similar to both EuIr4In2Ge4 and the parent structure Ca3Ir4Ge4, suggesting that these compounds comprise a new family of hybridization gap materials that exhibit indirect gap, semi-conducting behavior at a valence electron count of 60 per formula unit, similar to the Heusler alloys.</P>