The kesterite stannite structural transition as a way to avoid Cu Zn disorder in kesterites the exemplary case of the Cu2 Zn,Mn SnSe4

The solid solution series between Cu2ZnSnSe4, crystallizing in the kesterite type structure, and Cu2MnSnSe4, adopting the stannite type structure, i.e. Cu2(Zn1−xMnx)SnSe4, was studied by a combination of neutron and X-ray powder diffraction. Powder samples with 0 ≤ x ≤ 1 were synthesized by the solid state reaction of the pure elements and it was confirmed by wavelength-dispersive X-ray spectroscopy that each contained a homogeneous, off-stoichiometric quaternary phase. The lattice parameters and cation site occupancy factors were determined simultaneously by the Rietveld analysis of the neutron and X-ray powder diffraction data. The refined site occupancy factors were used to determine the average neutron scattering length of the cation sites in the crystal structure of the Cu2(Zn1−xMnx)SnSe4 mixed crystals, from which a cation distribution model was derived. For the end member Cu2ZnSnSe4, the disordered kesterite structure was confirmed and for Cu2MnSnSe4, the stannite structure was confirmed. The cross-over from the kesterite to stannite type structure by Zn2+ ↔ Mn2+ substitution in the Cu2Zn1−xMnxSnSe4 solid solution can be seen as a cation re-distribution process among the positions (0, 0, 0), (0, ½, ¼) and (0, ¼, ¾), including Cu+, Zn2+ and Mn2+. The Sn4+ cation does not take part in this process and remains on the 2b site. Moreover, the cross-over is also visible in the ratio of the lattice parameters c/(2a), showing a characteristic dependence on the chemical composition. The order parameter Q, the quantitative measure of Cu/BII disorder (BII = Zn and Mn), shows a distinct dependence on the Mn/(Mn + Zn) ratio. In Zn-rich Cu2(Zn1−xMnx)SnSe4 mixed crystals, the order parameter Q ∼ 0.7 and drops to Q ∼ 0 (complete Cu/BII disorder) in the compositional region 0.3 ≥ x ≥ 0.7. In Mn-rich Cu2(Zn1−xMnx)SnSe4 mixed crystals, adopting the stannite type structure, the order parameter reaches almost Q ∼ 1 (order). Thus, it can be concluded that only Mn-rich Cu2(Zn1−xMnx)SnSe4 mixed crystals do not show Cu/BII disorder. A similar trend of the dependence on the chemical composition of both Cu/BII-disorder and the band gap energy Eg in Cu2(Zn1−xMnx)SnSe4 mixed crystals was observed

The second law and beyond in microscopic quantum setups

The Clausius inequality (CI) is one of the most versatile forms of the second law. Although it was originally conceived for macroscopic steam engines, it is also applicable to quantum single particle machines. Moreover, the CI is the main connecting thread between classical microscopic thermodynamics and nanoscopic quantum thermodynamics. In this chapter, we study three different approaches for obtaining the CI. Each approach shows different aspects of the CI. The goals of this chapter are: (i) To show the exact assumptions made in various derivations of the CI. (ii) To elucidate the structure of the second law and its origin. (iii) To discuss the possibilities each approach offers for finding additional second-law like inequalities. (iv) To pose challenges related to the second law in nanoscopic setups. In particular, we introduce and briefly discuss the notions of exotic heat machines (X machines), and "lazy demons".Comment: As a chapter of: F. Binder, L. A. Correa, C. Gogolin, J. Anders, and G. Adesso (eds.), "Thermodynamics in the quantum regime - Recent Progress and Outlook", (Springer International Publishing). v1 does not include references to other book chapter

Thermodynamic principles and implementations of quantum machines

The efficiency of cyclic heat engines is limited by the Carnot bound. This bound follows from the second law of thermodynamics and is attained by engines that operate between two thermal baths under the reversibility condition whereby the total entropy does not increase. By contrast, the efficiency of engines powered by quantum non-thermal baths has been claimed to surpass the thermodynamic Carnot bound. The key to understanding the performance of such engines is a proper division of the energy supplied by the bath to the system into heat and work, depending on the associated change in the system entropy and ergotropy. Due to their hybrid character, the efficiency bound for quantum engines powered by a non-thermal bath does not solely follow from the laws of thermodynamics. Hence, the thermodynamic Carnot bound is inapplicable to such hybrid engines. Yet, they do not violate the principles of thermodynamics. An alternative means of boosting machine performance is the concept of heat-to-work conversion catalysis by quantum non-linear (squeezed) pumping of the piston mode. This enhancement is due to the increased ability of the squeezed piston to store ergotropy. Since the catalyzed machine is fueled by thermal baths, it adheres to the Carnot bound. We conclude by arguing that it is not quantumness per se that improves the machine performance, but rather the properties of the baths, the working fluid and the piston that boost the ergotropy and minimize the wasted heat in both the input and the output.Comment: As a chapter of: F. Binder, L. A. Correa, C. Gogolin, J. Anders, and G. Adesso (eds.), "Thermodynamics in the quantum regime - Recent Progress and Outlook", (Springer International Publishing

Insertion and Substitution Chemistry at the Boron Fourth Position in Charge-Neutral Zwitterionic Tripodal Tris(methimazolyl)borate Ligands

A number of new charge-neutral zwitterionic tris(methimazolyl)borate ligands have been synthesized, either by substitution of the dimethylamine group in the adduct (dimethylamine)tris(methimazolyl)borane (1) or by insertion into its B–N(dimethylamine) bond by an unsaturated Lewis base. Two new anionic ligands, (thiocyanato)tris(methimazolyl)borate and (cyano)tris(methimazolyl)borate, have also been accessed by this method

Energetic instability of passive states in thermodynamics

Passivity is a fundamental concept in thermodynamics that demands a quantum system’s energy cannot be lowered by any reversible, unitary process acting on the system. In the limit of many such systems, passivity leads in turn to the concept of complete passivity, thermal states and the emergence of a thermodynamic temperature. Here we only consider a single system and show that every passive state except the thermal state is unstable under a weaker form of reversibility. Indeed, we show that given a single copy of any athermal quantum state, an optimal amount of energy can be extracted from it when we utilise a machine that operates in a reversible cycle. This means that for individual systems, the only form of passivity that is stable under general reversible processes is complete passivity, and thus provides a physically motivated identification of thermal states when we are not operating in the thermodynamic limit

Cu2ZnGe S1 xSex 4 The challenge to synthesize single phase material

The variation of the band gap energy in Cu2ZnGeSe4 and Cu2ZnGeS4 from 1.4 eV to 1.7 eV, which is controlled by different S S Se ratios renders the Cu2ZnGe S1 xSex 4 solid solution an interesting material for the application in multi junction solar cells. Nevertheless, this system has a certain complexity due to the existence of different polymorphs. Cu2ZnGeSe4 crystallizes in the tetragonal kesterite type structure, whereas Cu2ZnGeS4 may crystallize in the tetragonal stannite or the orthorhombic wurtz stannite type structure, respectively. To gain deeper insights into this complex system a systematic study of the solid solution series Cu2ZnGe S1 xSex 4 was performed using polycrystalline material prepared by solid state reaction. The chemical analysis performed by wavelength dispersive X ray spectroscopy showed remarkable inhomogeneities with different quaternary phases co existing within one sample. Additionally, a wide variety of binary and ternary secondary phases as well as elemental Ge was observed. The variety of secondary phases is higher in S rich samples than in Se rich samples of the solid solution. Thus, synthesis of Cu2ZnGe S1 xSex 4 mixed crystals with off stoichiometric composition is readily accompanied by the formation of various secondary phases making it a difficult task to obtain single phase materia

Challenges and structural characterization of the solid solution Cu2Zn GexSi1 x Se4

The quaternary chalcogenides Cu 2 ZnSiSe 4 and Cu 2 ZnGeSe 4 crystallize in the orthorhombic wurtz stannite and tetragonal kesterite type structures, respectively. To investigate thestructural transformation within the solid solution series Cu 2 Zn Ge x Si 1 x Se 4 a systematic structural study was performed. Polycrystalline samples, prepared by solid state reaction, show a single quaternary phase as analyzed by WDX spectroscopy. Structural parameters of the mixed crystals were obtained using powder X ray diffraction. It can be shown that apart from Cu 2 ZnSiSe 4 , Si rich mixed crystals of this series adopt the wurtzstannite type structure. The lattice parameters are in consistency with Vegard s law and increase with increasing Ge conten