Dedicated to Professor Rudolf Hoppe on the occasion of his 90th birthdayThe prediction and identification of stable and particularly of metastable compounds is important in achieving innovative materials. [1] With this objective in mind, approaches containing both theoretical examinations of phase stabilities and concepts of a rational synthesis [2] are gaining increasing importance. Thus, an investigation of energy landscapes [3] provides important information about local and global minima to predict the existence of new compounds and structures.Herein, we introduce a combination of quantum-chemical calculations and thermodynamic considerations to realize target-oriented planning and optimization of chemical synthesis. The analysis of phase formation is acquired with an in situ method for monitoring gas-phase reactions. Using the system P-As, we investigated a textbook example of monotropic phase transitions, which features a variety of known and postulated allotropes. [4] To estimate the relative stabilities of the compounds under discussion, structure allotropes of N, P, and As were modeled by means of DFT calculations. The calculated electronic energies (normalized to one atom Pn) for molecular Pn 2 and Pn 4 , the black/orthorhombic (o-Pn), gray/ trigonal (t-Pn), and the simple-cubic (c-Pn) allotrope as well as the tubular polymeric forms of Hittorf (H-Pn), [5] Ruck (R-Pn), [6] and Pfitzner (P-Pn), [7] which are known for phosphorus, are shown in Figure 1. The high stability of N 2 can be observed as well as the preference for solid-state structures for P and As. Figure 1 b emphasizes the results for the t and o forms of P and As. The known stability of o-P compared to the high-pressure modifications t-P and c-P is correctly predicted as well as the stability of gray t-As compared to the known high-pressure modification c-As, hypothetical tubular As allotropes, and predicted o-As. Does this mean that o-As can be synthesized as a metastable compound? [8a] The calculated values of the total electronic energies correctly express the higher stability of o-P compared with the high-pressure phase t-P and also t-As compared to o-As. From the computed values DE el = E el (o)ÀE el (t) of À4 kJ mol À1 for P and + 2.5 kJ mol À1 for As, a transition from the o-to the tstructure in the ideal solution As x P 1Àx can be estimated to be about x = 0.6 ( Figure 2). Taking thermodynamic energy terms into consideration (for details, see the Supporting Information), a distinctive stabilization of the o phase is calculated and the o-t transition shifts to a higher As content (x = 0.9). According to the calculated values, very low energy differences decide whether or not o-As can actually be synthesized. [8b]

The application areas of rechargeable Li-ion batteries continue to grow, hence improvement in their energy density, rate capability and cycle life is necessary. A typical cathode contains usually redox active transition metal oxides as active materials, conductive additives to ensure electronic conductivity and binder supporting matrix. In this work we report the behavior and properties of carbon black free LiFePO 4 composite electrode, where poly (3,4-ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) is accomplishing a dual role of binder and conducting additive. The effect of the polymer amount on the morphometric properties of the electrodes was studied using SEM, mercury porosimetry and high resolution X-ray computed tomography. The electrochemical performance and the cycling stability of the composite electrodes were compared to the behavior of conventional cathodes with carbon additives and PVDF binder. With increasing PEDOT:PSS content a decrease in the overvoltage and correspondingly an improvement in the rate capability is observed. Composite cathodes containing 8% PEDOT:PSS show comparable electrode capacity and better cyclic stability than conventional composite cathode.

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Thermoelectric and phase analytical measurements were performed to investigate the physical properties of trimorphic Ag5Te2Cl. The material is a mixed electron/silver ion conductor featuring drastic property changes during a silver order/disorder phase transition at 334 K. The transition is characterized by a jump in the total electric conductivity by 2 orders of magnitude directly affecting the electric and thermoelectric properties. Silver ions are arranged in well-defined strands along the crystallographic c-axis characterized by a set of not fully occupied sites. Heat capacity measurements show a large effect, whereas the thermopower and thermal diffusivity drop significantly at the temperature of transition. Right after the transition, an attractive d10−d10 interaction within the disordered silver substructure occurs affecting the c-lattice parameter upon heating. Due to this interaction a modulation of the electronic structure and the thermoelectric properties can be observed which have been investigated in detail. While the thermopower stays low with increasing temperature the thermal diffusivity relaxes fast to values before the transition. At 355 K, the thermopower starts rising again, which is consistent with a small effect in the heat capacity and a reduction of the c-lattice parameter upon heating. Further heating leads to a reduction of the d10−d10 interactions and a drastic increase in the thermopower. The observed phenomenon must be regarded as a new example of a compound following the recently discovered concept of low-dimensional partially covalent-bonded structure units that can positively influence thermoelectric properties in bulk materials. Ag5Te2Cl is the first example where mobile d10 ions interact to create low-dimensional partially covalent-bonded subunits in a solid, which then leads to a switching of thermoelectric and electronic properties. The system shows very low thermal conductivities between 0.19 W m−1 K−1 and 0.60 W m−1 K−1 in the temperature range 298 to 500 K, reaching a maximal ZT value of 0.033 at high temperatures.

The ternary Laves phase Cd(4)Cu(7)As is the first intermetallic compound in the system Cu-Cd-As and a representative of a new substitution variant for Laves phases. It crystallizes orthorhombically in the space group Pnnm (No. 58) with lattice parameters a = 9.8833(7) Å; b = 7.1251(3) Å; c = 5.0895(4) Å. All sites are fully occupied within the standard deviations. The structure can be described as typical Laves phase, where Cu and As are forming vertex-linked tetrahedra and Cd adopts the structure motive of a distorted diamond network. Cd(4)Cu(7)As was prepared from stoichiometric mixtures of the elements in a solid state reaction at 1000 °C. Magnetic measurements are showing a Pauli paramagnetic behavior. During our systematical investigations within the ternary phase triangle Cd-Cu-As the cubic C15-type Laves phase Cd(4)Cu(6.9(1))As(1.1(1)) was structurally characterized. It crystallizes cubic in the space group Fd3m with lattice parameter a = 7.0779(8) Å. Typically for quasi-binary Laves phases Cu and As are both occupying the 16c site. Chemical bonding, charge transfer and atomic properties of Cd(4)Cu(7)As were analyzed by band structure, ELF, and AIM calculations. On the basis of the general formula for Laves phases AB(2), Cd is slightly positively charged forming the A substructure, whereas Cu and As represent the negatively charged B substructure in both cases. The crystal structure distortion is thus related to local effects caused by Arsenic that exhibits a larger atomic volume (18 Å(3) compared to 13 Å(3) for Cu) and higher ionicity in bonding.

Professor Rudolf Hoppe zum 90. Geburtstag gewidmet Die Vorhersage und Identifizierung von stabilen und besonders von metastabilen Phasen ist ein wichtiges Instrument zur Realisierung innovativer Materialien. [1] Mit dieser Zielsetzung werden zunehmend Lçsungsansätze verfolgt, die sowohl theoretische Betrachtungen der Phasenstabilität als auch Konzepte einer gezielten Synthese [2] einbeziehen. So liefert eine Untersuchung der Energielandschaft [3] wichtige Erkenntnisse über lokale und globale Minima zur Existenz mçglicher Verbindungen und Strukturen.Im Folgenden werden wir zeigen, wie die Kombination von quantenchemischen Rechnungen und thermochemischen Betrachtungen zielgerichtet für eine Syntheseplanung und -optimierung eingesetzt werden kann. Die Analyse der Phasenbildung gelingt mit einer In-situ-Methode zur Verfolgung von Gasphasenreaktionen. Wir haben uns mit dem System P-As als einem Lehrbuchbeispiel für monotrope Phasenumwandlungen befasst, das durch eine Vielzahl von bekannten und postulierten Allotropen [4] bestimmt wird.Zur Abschätzung relativer Stabilitäten wurden mithilfe von DFT-Rechnungen allotrope Strukturen von N, P und As modelliert. In Abbildung 1 sind die berechneten elektronischen Energiewerte (normiert auf 1 Atom Pn) für molekulares Pn 2 und Pn 4 , das schwarze/orthorhombische (o-Pn), graue/trigonale (t-Pn) und kubische Allotrop (k-Pn), sowie die vom Phosphor bekannten rçhrenartigen polymeren Formen nach Hittorf (H-Pn), [5] Ruck (R-Pn) [6] und Pfitzner (P-Pn) [7] aufgetragen. Sie zeigen die hohe Stabilität des N 2 sowie die Bevorzugung der Festkçrperstrukturen bei P und As. Abbildung 1 b stellt die Ergebnisse zu den t-und o-Formen von P und As heraus. Die bekannte Stabilität für o-P gegenüber den Hochdruckformen t-P und k-P wird ebenso korrekt vorhergesagt wie die des grauen t-As gegenüber der bekannten Hochdruckform k-As, bisher nicht bekannten rçhrenartigen As-Allotropen und des angenommenen o-As. Ist o-As als metastabile Verbindung damit synthetisierbar? [8a] Die berechneten elektronischen Energiewerte sagen die hçhere Stabilität von o-P gegenüber der Hochdruckphase t-P, bzw. von t-As gegenüber o-As korrekt vorher. Aus den berechneten Werten DE el = E el (o)ÀE el (t) von À4 kJ mol À1 (P) und + 2.5 kJ mol À1 (As) lässt sich für die ideale Lçsung As x P 1Àx ein Übergang von der o-zur t-Struktur bei x = 0.6 abschätzen (Abbildung 2). Die Berücksichtigung thermodynamischer Energieterme (siehe die Hintergrundinformationen) zeigt eine stärkere Stabilisierung der o-Phase und damit Abbildung 1. a) Berechnete Gesamtenergien (0 K) der Element-Allotrope, normiert auf ein Atom Pn (Pn = N, P und As). b) Vergrçßerter Ausschnitt ausgesuchter Allotrope. (Pn 4 = molekulares Pn 4 , k = kubisch, o = orthorhombisch, t = trigonal, H = Hittorf, R = Ruck, P = Pfitzner)

Coinage-metal(I) polychalcogenide halides represent a new class of materials featuring high ion dynamics of different substructures capable of an effective phonon scattering process in the solid state. The interplay of mobile coinagemetal ions such as Ag + or Cu + on the one hand and the temperature-driven redox reaction of a linear, partially covalent-bonded Te chain on the other hand is responsible for tremendous variations in the electronic structure of such materials. A huge drop of the Seebeck coefficient within a very small temperature range and an extremely low thermal conductivity are the key properties of Ag 10 Te 4 Br 3 , the first representative of this substance class. Two different sets of compounds with the general formula (CM) 10 Q 4 X 3 and (CM) 23 Q 12 X (CM = coinage metal Cu or Ag, Q = chalcogen, X = halogen) have been found, and recent experiments point toward the existence of formerly unknown copper(I) (poly)chalcogenide halides and two more silver(I) (poly)chalcogenide halides in this field. A comparable linear Te chain is present in a number of different compounds such as some alkaline-earth polychalcogenides M 5 Te 3 , the mineral stuetzite Ag 4.5 Te 3 , and the closely related compounds Ag 11 AsTe 7 and Ag 12 Te 6 S. In most cases the thermoelectric potential of these materials has not been verified. A topological approach for the description of the structural features has been developed to understand the electronic properties of these complex materials in detail.

Nominal In4Se3–x with x = 0.65, derived from the prototype compound In4Se3, is a good thermoelectric material achieving a Z value of 1.48 at 705 K. This value is close to state of the art thermoelectric materials. In literature this special behavior is explained by a Peierls‐distortion or Charge Density Wave within the compound caused by the selenium deficit. While extensive thermoelectric studies for different compositions are reported in literature, a solid proof of the existence of selenium deficit samples is still missing. In this work we report about the synthesis, phase analyses, and temperature dependent single crystal determinations of In4Se3–x samples in order to clarify these structural features.