Investigation of Thermoelectric Thallium Chalcogenides

Thermoelectric materials have drawn extensive attention because of their potential to provide assistance in reducing the usage of fossil fuel sources and the greenhouse effect. Throughout this thesis, the purpose was to investigate the thermoelectric properties of previously reported thallium tellurides. Tl2Ag12Te7+δ, TlSbTe2, and Tl4Ag18Te11 were selected as candidates for this investigation due to their interesting crystal structures. By substituting the Te element in Tl2Ag12Te7+δ, with Se we found a new phase of Tl-Ag-Se system which crystallizes in a commensurate superstructure and possesses ultralow thermal conductivity. These four parent compounds have low thermal conductivity owing to the high molar mass and complex crystal structures. In Chapter 1, thermoelectric background knowledge was introduced. Generally, complex crystal structures such as incommensurate superstructures can reduce the lattice thermal conductivity, which is beneficial for increasing the thermoelectric figure of merit. The minimum lattice thermal conductivity can be estimated by three different models: Clarke model, Cahill model, and Diffuson model. Finally, a brief review of the state-of-the-art chalcogenide thermoelectrics was presented. In Chapter 2, the experimental procedures related to all the projects were described. Powder X-ray diffraction, single crystal X-ray diffraction, and energy depressive X-ray analysis were utilized to obtain the compositional and structural information of the synthesized materials. Electronic structures of the materials were determined by performing first principle density functional theory calculations. Then the physical properties including melting point, Seebeck coefficient, electrical conductivity, and thermal conductivity were determined. In Chapter 3, a new selenide, Tl2Ag12Se7, is reported. Unlike Tl2Ag12Te7+δ, Tl2Ag12Se7 crystallizes in a commensurate superstructure with a √3 × √3 × 1 super cell of the Zr2Fe12P7 structure type. Initial investigations into the thermoelectric properties of this selenide suggested that it was a p-type semiconductor at room temperature that underwent a pnp phase transition at 410 K. Further investigations via XPS indicated that the electronic states of all atoms did not undergo significant variations before and after the phase transition temperature. The reanalysis of the raw data obtained from the ZEM-3 instrument and the low temperature Seebeck measurements implemented by the PPMS also confirmed that Tl2Ag12Se7 remains a p-type semiconductor throughout all temperatures investigated. In Chapter 4, Tl2Ag12Te7+δ was originally reported by Moreau et al. to crystallize in the hexagonal space group P6.1 The unrealistically short Te-Te bond distances in the reported crystal structure (2.4 Å) led us to investigate the crystal structure further. We determined that Tl2Ag12Te7+δ is actually an incommensurate composite crystal structure composed of a linear Te atom chain along the c axis surrounded by a Tl2Ag12Te6 framework. The super-space group of the Te atom chain is P6(00γ)s and the super-space group of the Tl2Ag12Te6 framework is P63(00γ)s. The complex crystal structure resulted in an extremely low thermal conductivity of 0.25 W m–1 K–1 and a zT of 1.1 at 525 K. This is the largest thermoelectric figure of merit observed in an incommensurate crystal structure to date. In Chapter 5, the TlSbTe2 crystal structure shares similarities with the crystal structure of the state of the art thermoelectric material Bi2Te3. Both have a layered crystal structure; this layered structure in Bi2Te3 leads to anisotropic electronic properties depending along which crystallographic axis the properties are measured. TlSbTe2 has significantly more covalent interactions between the telluride layers diminishing the anisotropic effects. The best thermoelectric performance of In-doped TlSbTe2 was achieved at 625 K, with a figure of merit (zT) of 0.77. The overall best zT was improved to 0.85 at 620 K with the sample of nominal composition Tl0.98SbYb0.02Te2. In Chapter 6, Tl4Ag18Te11 was claimed to crystallize in a cubic structure with disordered Tl atoms filling cuboctahedral voids. The electronic structure calculations of Tl4Ag18Te11 predicted it to be a semimetal with the valence and conduction bands touching at the Γ point in the Brillouin zone, based on an I4mm space group model with ordered Tl atom sites. The studies of the thermoelectric properties of hot-pressed Tl4Ag18Te11 and its nonstoichiometric homologs, illustrated an unusual n-type extrinsic semiconducting behavior, combined with an extremely low thermal conductivity. The thermal conductivity of a sample of the nominal composition “Tl4.05Ag18Te11” reached 0.19 W m−1 K−1 at 500 K, with this value being one of the lowest achieved by crystalline materials to date. This can be attributed to the highly disordered Tl atoms and the large unit cell with its highly complex structure, in accord with the low Debye temperature of 98 K

Optimization of Thermoelectric Chalcogenides

Thermoelectric (TE) materials can convert heat into electricity when a temperature gradient is applied (Seebeck effect), and can pump heat from the cold end to the hot end using electricity (Peltier effect). These materials have shown improved properties in recent years, and promising bulk materials have been uncovered by many research groups. Chalcogenide containing materials are the leading TEs today, and examples uncovered by the Kleinke group include Tl4(Zr,Hf)Te4, Ba3Cu16–xS11–yTey, and BaCu6-x(S,Se)Te6. Initial evaluation of cold-pressed pellets of these materials showed potential for TE application, with a high figure-of-merit, zT, which relates to the efficiency of a material in converting heat into electricity. This zT is a dimensionless figure composed of heat and electrical transport properties of a material through the equation: zT=〖Tα〗^2 σκ^(-1), where α is the Seebeck coefficient, σ the electrical conductivity, and κ the thermal conductivity, measured at a specific temperature (T). A zT value above unity is desired for a bulk material to be used for power generation. The biggest challenge in optimizing TE materials is decoupling the properties contributing to zT, and tuning the properties in a way that improves the zT overall. In this work, it is demonstrated that the zT value for a material can be improved through doping and hot pressing to close to ideal density. Adding Nb to Tl4ZrTe4 improved the zT compared to the ternary sample by enhancing the electrical conductivity. The zT of the samples of nominal composition "Tl4ZrNb0.04Te4" and Tl4Zr1.03Te4 amounted to 0.064 and 0.042 at ~500 K, respectively. Properties of undoped Tl4HfTe4 were also compared to those of Tl4Zr1.03Te4, and Tl4HfTe4 had a higher zT of 0.08 at ~480 K, which is however still too low for any application. Varying the x and y values in Ba3Cu16–xS11–yTey achieved the highest zT for Ba3Cu15.1S8Te3, amounting to 0.78 at ~780 K. However, after six repeat electrical property measurements, these samples showed color change, which was confirmed, via EDX measurement, to be the result of Cu atoms migrating across the material. In contrast, BaCu6-x(S,Se)Te6 showed great stability after repeat measurements, which is attributed to localized mobility of Cu atoms. The properties of BaCu6-x(S,Se)Te6 were measured, and zT values of 0.52 at 580 K and 0.81 at 600 K were obtained for BaCu5.9STe6 and BaCu5.9SeTe6, respectively.4 month

Thermoelectric Properties of Chalcogenide System

We will discuss the development of a new ternary and quaternary tellurium telluride chalcogenide nanoparticles used for efficient thermo-electric waste heat energy convertor called thermo-electric generator. Nanoparticles-based tellurium telluride chalcogenide nanoparticles, which will be used for thermoelectric generator, will eventually solve an important issue of the energy crises, that is, conversion of waste heat into useful electrical energy. By injecting charge carriers in the host matrix of Tl10-x-yAxByTe6 nanomaterials system, different types of dopants (A = Pb, Sn, Ca and B = Pb, Sb Sr, etc.), with x = 0–2.5 and y = 0–2.5 on tellurium telluride has been introduced to synthesize new materials by Co-precipitation techniques and also by solid state reaction techniques followed by Ball-Milling for the fabrication of nanomaterials. We will study the effect of reduction of charge carriers in thermal and transport properties using different dopants contents by replacing host atoms. The charge carrier’s concentration will affect the ratio of electron-hole concentration which in turns increases the electron scattering in these chalcogenide nanoparticles, which will affect the electrical conductivity and thermo-power. The prime purpose of doping with different ionic radii and different concentration is to enhance the power factor for the tellurium telluride nanosystem. At the end one will be able to control different physical parameters such as, thermally assisted electrical conductivity, and thermopower. Different characterization technique will be applied, for example, X-Ray diffraction techniques will be used for structural analysis, SEM will shows the morphological structure of the particles at 100 nm and energy dispersive x-rays spectroscopy will be used for elemental analysis. The electrical conductivity will be measured by four-probe resistivity measurement techniques, and Seebeck coefficient will be measured by standard temperature gradient techniques

Exploration and Optimization of Tellurium-Based Thermoelectrics: Property enhancements through heavy p-block inclusions and complex bonding.

Thermoelectric materials are the only known materials capable of direct conversion of a heat gradient into electricity (Seebeck effect) or vice-versa (Peltier effect). Thermoelectric (TE) devices are comprised of solid-state p-type and n-type semiconductors paired in an electrical circuit and exposed to a temperature gradient. The effectiveness of the materials is evaluated based on the mathematical term ZT=T∙S^2 σ/κ: S represents the Seebeck coefficient; σ represents the electrical conductivity; κ is the thermal conductivity; and T is the average of the coldest and hottest regions of the applied gradient. This ZT term is larger for better materials; most modern devices in use to-date display ZT values on the order of one. A large temperature gradient combined with a large Z term will lead to a high-performance TE material that involves no waste, no side product, and no requirement for moving parts. Discovery and optimization of new thermoelectric materials is a critical component of current thermoelectric research. As such, researchers are constantly searching for a new material that has the following properties: the ability to withstand higher temperatures, thus maximizing the T term; exhibit a large Seebeck coefficient and electrical conductivity through doping techniques; and present minimal thermal conductivity, κ. In recent years, research attention has moved from S^2σ to κ, which can be optimized through a variety of techniques including complex crystal structure, heavy element inclusion, and introduction of structural defects such as nanodomains/nanostructuring. Due to their tendency to form complex crystal structures and bonding, Te-based materials have become popular targets for TE research and optimization. Compounds with Te anions that also include other heavy elements such as alkali (A) metals, alkaline earth (R) elements, or heavy p-block elements including the triels (Tr), tetrels (Tt), or pnictogens (Pn) have become a principal source of new and ground-breaking thermoelectric materials. Likewise, optimization of existing TE materials with these aforementioned compositions has led to ZT values twice those of the materials' original reports. Of the known TE materials, Bi2Te3 is one of the staples in the field. It shows narrow band-gap semiconducting properties that can be tuned to p- or n-type values based on the impurities introduced, and its κ values are inherently low due to the presence of heavy elements and their structural layering motifs. A series of compounds, (SnTe)x(Bi2Te3)y, based on this idea can be produced via the alteration of x:y. In this work, several of these compounds are introduced and studied as potentially useful thermoelectric materials: SnBi2Te4, SnBi4Te7, and SnBi6Te10 are the major targets because of their systematic layering motifs and complex structures. Phase range studies, crystal structure (Rietveld) refinements, and synthesis optimizations were commenced to ensure that the materials were well-characterized and produced phase-pure before the attempted ZT improvements. By altering the quantity of active charge carriers in these systems, changes in ZT can be observed – this is achieved through doping with, primarily, heavy Tr elements Ga, In, and Tl. Thusly, the physical properties are measured and compared for a number of series: [Tr]xSn1-xBi2Te4, [Tr]xSnBi2-xTe4, [Tr]xSn1-xBi4Te7, [Tr]xSnBi4-xTe7, [Tr]xSn1 xBi6Te10, and [Tr]xSnBi6-xTe10. Of the triels, Tl is the largest useful element in the group and is known for showing both Tl+ and Tl3+ cationic states and, in thermoelectric applications, for possessing uniquely low κ values. Thallium telluride compounds such as Tl5Te3 are therefore quite relevant to this field. The family of compounds includes Tl9BiTe6 – one of the better materials with ZT = 1.2 (500 K) using a hot-pressed pellet. Herein, the system is expanded to include Tl10-xSnxTe6 which shows good TE potential with ZT(Tl7.8Sn2.2Te6) = 0.6 (617 K) with a cold-pressed pellet. The incorporation of tetrel elements is investigated through measurements on Tl10-x-ySnxBiyTe6 and also applies to the lesser-studied Tl9SbTe6 compound via research on the systems Tl9SnxSb1 xTe6 and Tl9PbxSb1 xTe6. Tl is studied in three concentrations with Tl10 x ySnxBiyTe6: Tl9…, Tl8.67…, and Tl8.33…, with varying Sn:Bi at each increment. Tt elements are systematically added to the Tl9[Tt]xSb1 xTe6 structure with 0.0 ≤ x ≤ 0.7. Crystallographic studies, electronic structure calculations, and physical properties are explored for each series. Due to Te’s ability to form complex Te–Te interactions in certain environments, the combination of alkaline earth metals, namely R = Ba, with the coinage metals (Cg = Cu, Ag), chalcogenides (Q = S, Se), and Te, form a plethora of previously unknown crystal structures. Many of these are Zintl-phase narrow-band gap semiconductors with complex Cg–Cg and Q–Q bonding schemes – combined with their heavy element incorporation, the family is of great interest to the thermoelectrics community. Within this thesis, three new crystal systems are presented: Ba3Cu17-x(Se,Te)11; Ba3Cu17-x(S,Te)11 and Ba3Cu17-x(S,Te)11.5; and Ba2Cu7-xTe6. All structures show Cu-deficiencies in their crystal structures with d10–d10 interactions and 3-dimensional networks of the Cg metal. The chalcogenide elements in the structures display unique Q–Q or Te–Te bonding of varying dimensionality. The electronic structures and bonding calculations are reported for each compound, as are the single crystal studies. The first two of the aforementioned compounds are narrow-band gap semiconductors, whereas the latter two display metallic behaviour

Thallium Tellurides as Thermoelectrics

Noting the steadily worsening problem of depleted fossil fuel sources, alternate energy sources become increasingly important, such as thermoelectrics that may use waste heat to generate electricity. To be economically viable, the thermoelectric figure-of-merit, zT, – related to the energy conversion efficiency – needs to be in excess of unity (zT > 1). Modifications of Tl5Te3 show great promise as thermoelectrics due to their intrinsically low thermal conductivity. Herein thallium lanthanide tellurides Tl9LnTe6 (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb) have been prepared and their high temperature electrical and thermal transport properties investigated. Single phase samples were obtained. The electrical conductivity and thermal conductivity increased across the lanthanide series from La to Tb. On the other hand, the Seebeck coefficient values decreased with Ln varying from La to Tb. Tl9SmTe6 or Tl9GdTe6 constituted an exception, as the Seebeck coefficient of Tl9SmTe6 was smaller than that of Tl9GdTe6. Tl9LaTe6 had the largest figure-of-merit zT = 0.51 at 550 K. Thereafter, Tl10–xLaxTe6 samples were prepared with x = 0.90, 0.95, 1.00, 1.05, 1.10, aiming toward higher zT through composition optimization and expanding of the measurement temperature range. With the increasing La content, the unit cell volume increased, while the electrical conductivity, thermal conductivity and lattice thermal conductivity decreased. An opposite trend between Seebeck coefficient and electrical conductivity was observed. The highest zT = 0.57 was realized for Tl9LaTe6 at 600 K. The isostructural series Tl9Sb1–xTe6, Tl9–xSb1+xTe6, Tl9Bi1–xTe6 and Tl9–xBi1+xTe6, with x ranging from 0 to 0.05, were prepared from the elements in the stoichiometric ratios, and the thermoelectric properties determined. In theory, these tellurides are narrow gap semiconductors when x = 0, with all elements in common oxidation states, according to (Tl+)9(Sb3+/Bi3+)(Te2–)6. The as-prepared samples of this 9-1-6 stoichiometry however exhibited relatively high electrical conductivity, which decreased with increasing temperature, indicative of the presence of extrinsic charge carriers. The Seebeck coefficient was generally above +100 μV K–1. Decreasing the Sb or Bi content then increased the hole concentration, and thus increased the electrical conductivity while decreasing the Seebeck coefficient. The best feature of these thermoelectrics was their low thermal conductivity, being consistently well below 0.7 W m–1K–1. Combined with reasonable electrical conductivity and high Seebeck coefficient, high zT values in excess of 1 can be achieved via simple hot-pressing as well, after experimental optimization of the carrier concentration via introducing deficiencies on the Bi site. Moreover, the variants with Sb instead of Bi exhibited similar thermoelectric performance, a result of the combination of a better electrical performance and higher thermal conductivity. To investigate the effects of Sn- and Pb-doping, several samples with the nominal composition Tl9Bi1–xSnxTe6, Tl9Bi1–yPbyTe6 (0 ≤ x, y ≤ 0.15), Tl9Sb1–mSnmTe6 and Tl9Sb1–nPbnTe6 (0 ≤ m, n ≤ 0.10) were investigated. Thermoelectric property measurements showed that increasing doping caused increases in electrical and thermal conductivity, while decreasing the Seebeck coefficient. Mixed results were obtained for the lattice thermal conductivity, which decreased in some cases, but increased in others. At around 500 K, competitive zT values were obtained for Tl9Bi0.95Sn0.05Te6, Tl9Bi0.95Pb0.05Te6, Tl9Sb0.97Sn0.03Te6, and Tl9Sb0.95Pb0.05Te6, namely 0.95, 0.94, 0.83 and 0.71, respectively. Higher dopant concentrations led to lower zT values. The 8-2-6 variants Tl4SnTe3 and Tl4PbTe3 were reported to attain a thermoelectric figure-of-merit zTmax = 0.74 and 0.71 at 673 K, respectively. Here, the thermoelectric properties of both materials are presented in dependence of x in Tl10–xSnxTe6 and Tl10–xPbxTe6, with x varying between 1.9 and 2.05, culminating in zTmax values in excess of 1.2. These materials are charge balanced when x = 2, according to (Tl+)8(Sn2+)2(Te2–)6 and (Tl+)8(Pb2+)2(Te2–)6 (or: (Tl+)4Pb2+(Te2–)3). Increasing x caused an increase in valence electrons, and thus a decrease in the dominating p-type charge carriers. Thusly, larger x values occurred with a smaller electrical conductivity and a larger Seebeck coefficient. In each case, the lattice thermal conductivity remained under 0.5 W m–1K–1, resulting in several samples attaining the desired zTmax > 1. The highest values thus far are exhibited by Tl8.05Sn1.95Te6 with zT = 1.26 and Tl8.10Pb1.90Te6 with zT = 1.46 around 685 K. These materials are very competitive compared to other leading bulk materials as well, including the n-type triple-filled skutterudite Ba0.08La0.05Yb0.04Co4Sb12, the p-type Zintl phase Yb13.6La0.4MnSb11 and p-type Tl0.02Pb0.98Te until 673 K

Magnesium Silicide Based Thermoelectric Nanocomposites

The major objective of this thesis was to investigate how far the thermoelectric (TE) properties of magnesium silicide based materials can be enhanced via doping, alloying, and nanostructuring. The investigation of Sb and Bi doped Mg2Si showed experimentally that the dopants can indeed substitute Si in the crystal lattice. The excess Sb and Bi atoms were found in the grain boundaries, most likely in the form of Mg3Sb2 and Mg3Bi2. As a consequence, the sample showed lower carrier concentration than the formal Sb/Bi concentration suggests, and the thermal conductivity was significantly reduced. The investigation of the effect of germanium substitution for silicon in bismuth doped Mg2Si, showed that the alloying drastically reduced the room temperature thermal conductivity partially due to the added mass contrast and the existence of Ge-rich domains within the sample. Due to the increased in the amount of scattering centers caused by Ge alloying, the electrical conductivity was also decreased while the Seebeck coefficient was increased only very slightly. In summary, the positive effect of Ge substitution on the TE properties of Bi doped Mg2Si resulted in a figure of merit of 0.7 at 773 K for Mg2Si0.677Ge0.3Bi0.023 sample. The addition of multi wall carbon nanotubes (MWCNT) to the Mg2Si0.877Ge0.1Bi0.023 resulted in an improved electrical conductivity, in particular around room temperature. The Seebeck coefficient of all nanocomposites is enhanced at 773 K due to energy filtering that stems from the introduction of CNTs - Mg2Si0.877Ge0.1Bi0.023 interfaces. The lattice thermal conductivity of the nanocomposites is reduced due to the phonon scattering by nanodomains and grain, particularly at medium temperatures, resulting in a slight reduction in total thermal conductivity. All in all, the thermoelectric figure of merit of the sample containing 0.5 weight-% MWCNT was enhanced by about 22% as compared to the pristine sample. Finally, the investigation of the effect of silicon carbide (SiC) nanoparticles on the TE properties of Mg2Si0.676Ge0.3Bi0.024 revealed that increasing the concentration of SiC nanoparticles systematically reduced the electrical conductivity, while enhancing the Seebeck coefficient. In spite of its high thermal conductivity, SiC could successfully decrease the lattice thermal conductivity through adding more interfaces. The HRTEM study showed the existence of both Ge and Bi in the Si position, and some Bi segregation at the boundary. In summary, the figure of merit reached its maximum value of 0.75 at 773 K for the sample containing 0.5 wt.-% SiC, which is among the highest achieved in the Mg2Si1-xGex system

Strukturchemische Untersuchungen an Hexachalkogenohypodiphosphaten und verwandten Verbindungen

Der Schwerpunkt der Dissertation "Strukturchemische Untersuchungen an Hexachalkogenohypodiphosphaten und verwandten Verbindungen" liegt in der Synthese und kristallographischen Charakterisierung neuer Hexachalkogenohypodiphosphate. Die Verbindungen werden überwiegend durch Aufschmelzen und anschließendes Tempern stöchiometrischer Gemenge der reinen Elemente in evakuierten Quarz-Ampullen erhalten. Im Rahmen dieser Arbeit wurden insgesamt 39 Verbindungen kristallographisch untersucht. 10 Thiohypodiphosphate, 15 Selenohypodiphosphate und zwei verwandte Hypoditetrelverbindungen, Bi2Si2Te6 und In2Ge2Te6, werden detailliert auf Basis von Einkristall-Strukturanalysen und Pulverdiffraktometrischer Ergebnisse diskutiert. Die Arbeit zeigt erstmals die strukturchemische Verwandtschaft vieler Hypodiphosphate mit der Perowskit-Struktur auf. Ein formales Substitutions- und Verwandschafts-Schema hierzu wird in Kapitel 7 der Arbeit gegeben. Als Nebenaspekt der Arbeit gelingt die Klassifikation der Mehrzahl bekannter Hexachalkogenohypodiphosphate in zwei Strukturfamilien als Verbindungen mit vom Cadmiumhalogenid- bzw. vom Perowskit-Typ ableitbaren Struk¬turen. Es wird gezeigt, dass die Struktur von Ag3Tl5(P2S6)2 aus verschiedenen 3-dimensionalverknüpften Ketten aufgebaut wird. Ein anderer, komplexerer, Strukturtyp wird in der Verbindung Ag2Tl2P2Se6 erhalten. Es finden sich Anzeichen für schwache Ag-Tl und Ag-Ag-Wechselwirkungen. Analoge Anzeichen für Cu-Tl-Wechselwirkungen werden in den Verbindungen Cu2Tl2P2S6 und Cu2Tl2P2Se6 beobachtet. Die Cu-Verbindungen können darüber hinaus am besten als "gefüllter" Perowskit betrachtet werden. In dieser Arbeit wird erstmals gezeigt, dass die Strukturen vieler Hypodiphosphate als Substitutions- bzw. Ordnungs-Varianten der Perowskit-Struktur beschrieben werden können. Verschiedene solcher Ordnungsvarianten werden anhand der Ausordnung der Kationen unterschieden. Die zentrosymmetrischen Verbindungen der TlMP2Q6 Familie mit M = Ce, La und Q = S, Se sowie TlPrP2Se6 kristallisieren in der Raumgruppe P 21/c. Die nicht-zentrosymmetrischen Verbindungen der TlMP2Q6 Familie mit M = Bi, In, Sb und Q = S bzw. M = Sb, Dy, Er, Sm, Tb, Y und Q = Se kristallisieren in der Raumgruppe P 21. Die Verbindung TlBiP2Se6 stellt eine weitere Untervariante, eine zweifachen Überstruktur der zentrosymmetrischen TlMP2Q6 Familie, dar. Vier Verbindungen der MI4MIII2(PQ4)2P2Q6 Familie, die drei Sulfide mit MI = Tl und MIII = Sm, Y bzw. La und das Selenid mit MI = Tl und MIII = Er, wurden ebenfalls erhalten und vollständig strukturell charakterisiert. In den MI4MIII2(PQ4)2P2Q6 Verbindungen treten zwei unterschiedliche komplexe Anionen, [PQ4]3- and [P2Q6]4-, auf. Die Verbindungen kristallisieren in einer komplexen Struktur. Mittels Gruppe-Untergruppe Beziehungen wird ein vollständiger Bärnighausen-Stammbaum aller bekannten Verbindungen der MI4MIII2(PQ4)2P2Q6 Familie hergeleitet. Die Verbindungen AgMP2Se6 (M = Er, Sc, Tm) und alpha-CuBiP2Se6 erweitern die Zahl bekannter Hexachalkogenohypodiphosphate mit vom CdI2 abgeleiteten Strukturtyp in der Raumgruppe P -3 1 c. Anhand pulverdiffraktometrischer Daten wird gezeigt, dass CuScP2Se6 isostrukturell zu diesen CdI2-Varianten in der Raumgruppe P -3 1 c kristallisiert. Die Verbindung AgSbP2Se6 ist hingegen isostrukturell zu AgBiP2Se6 und zählt damit zu einer anderen Familie von mit dem CdI2-Typ verwandten Ver¬bin¬dun¬gen mit der Raumgruppe R -3. Die Struktur von AgBiP2Se6 wurde anhand eines doppelt meroedrisch verzwillingten Kristalls gelöst und stellt eine seltene Substitutionsvariante mit einer zweifachen Überstruktur mit verdoppelter c-Achse des M2P2Q6 Strukturtyps mit der Raumgruppe R -3 dar. Die zwei Hypoditetrelverbindungen Bi2Si2Te6 und In2Ge2Te6 kristallisieren ebenfalls in letzterem Strukturtyp. Diese Verbindungen sind nahe verwandt mit den sog. Phase-Change-Materialien wie z. B. Indium dotiertes Ge2Sb2Te5 und stellen daher möglicherweise interessante Beispielverbindungen für das Strukturverständnis und die strukturellen Prozesse in optischen Datenspeichermedien dar. CuScP2S6 ist die einzige Verbindung in dieser Arbeit, die in einer Variante des CdCl2-Typs mit einer monoklinen Elementarzelle und der Raumgruppe C 2/c kristallisiert. In CuScP2S6 tritt eine statistische Fehlordnung der Kupferatome auf zwei off-centre Positionen auf. Fehlordnungen dieser Art sind bei Kupferhypodiphosphaten dieses Typs ein verbreitetes Phänomen. Vier Verbindungen der TlMP2S7 Familie sind als Nebenprodukte in dieser Arbeit angefallen und wurden mittels Einkristallstrukturanalyse untersucht. Die Verbindungen mit M = Ce, Nd, Pr and Sc kristallisieren in zwei unterschiedlichen Strukturtypen und weisen das Pyrophosphat-Anion [P2S7]4- auf. Die Struktur des bereits bekannten HfSe2 wurde erstmals am Einkristall untersucht. Die bereits postulierte Verbindung AgCu2PS4 wurde ebenfalls am Einkristall strukturell charakterisiert. Es wird gezeigt, dass das quasi-binäre System Cu3PS4-Ag3PS4 eine Überstruktur mit geordneter Lagensubstitution der Silber- und Kupferatome bei der Zusammensetzung AgCu2PS4 aufweist. Weiterhin findet sich eine Liste von Hexachalkogenohypodiphosphaten und verwandten Verbindungen inklusive der zugehörigen Literaturstellen in Kapitel 8 dieser Arbeit in Form von übersichtlich gehaltenen Tabellen

Electromagnetic Field Radiation in Matter

This book is dedicated to the interaction of electromagnetic wave radiation in matter, such as the wave propagation in a plasmonic and conductive state, that are dispersive media. The different measurement methods of electrical properties of soils have been studied using several applications. The experimental results of the thermoelectric properties of a chalcogenide system and the electrical conductivity of molten salts and ionic conduction in electrolyte solutions are discussed. The application of an electric field impulse and its influence on the immune responses of animals by increasing different elements of the immune response is discussed. The electromagnetic radiation transmission through skin samples of pigs of different ages have been measured in order to understand the process of absorption and conversion. The methods and results are covered in the book

MBE GROWTH AND CHARACTERIZATION OF Pb-SALT SEMICONDUCTORS FOR MID-INFRARED DETECTOR AND LASER APPLICATION

IV-VI semiconductors grown by molecular beam epitaxy (MBE) on various substrates are extensively attractive for mid-infrared optoelectronic device application. The main goal of this research is to improve device performance by lowering defects densities in the epitaxial layers during MBE growth of Pb-salt materials on a lattice-mismatched substrate. Most of the work is based on MBE growth of monocrystalline PbSe on Si (111) substrates. Details of experiments are described and supported by reflection high-energy electron diffraction (RHEED) patterns. The effect of the in-situ surface treatment methods with a motivation of improving electrical and morphological properties of epilayers is demonstrated.A detailed study on surface morphologies and chemical composition of growth pits and dislocations in PbSe epilayers is provided. Various growth defects are investigated by scanning electron microscopy (SEM) and energy-dispersive x-ray analysis (EDXA). Through a series of experimental studies, it has been confirmed that the vast majority of growth pits within PbSe epilayers contains either single or multiple PbSe microcrystals with a distinct cuboid shape.Lead salt mid-infrared optoelectronic devices are fabricated on various substrates. Several other research works include: (1) Edge-emitting infrared lasers on BaF2 (110) substrates. A method of substrate transfer from a BaF2 substrate to a copper heat-sink is developed. Pulsed photoluminescence (PL) measurements are conducted with help of Fourier transform infrared (FTIR) spectroscopy method during every single step of device processing. (2) Mid-infrared detectors on silicon (111) substrates. Single-element PbSnSe infrared detectors have been made on CaF2 /Si (111) heterostructures; I-V measurement is accomplished on these detectors