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Response to the comments by P. Szakalos, T. angstrom kermark and C. Leygraf on the paper "Copper in ultrapure water, a scientific issue under debate"

The transformation within the solid state of tetragonal TlCu 5 Se 3 into the metastable orthorhombic form of TlCu 4 Se 3 by oxidative copper leaching in concentrated ammonia solution has been studied in situ by conventional X-ray powder diffraction. The ease with which the reaction occurs illustrates a comparatively high diffusion coefficient typical of copper sulphides and selenides. The diffraction patterns of the parent phase as well as the product remain sharp during the process, indicating strong topotaxy in the first-order transformation that is effectuated by the access of oxygen while the accompanying released copper enters the liquid phase. The transformation was followed in a real-time mode, leading to a complete transformation of the amount probed.

The possibility of copper reacting with O2-free water has been investigated by analysis of primary corrosion products, as well as by monitoring gas pressure change by time, in long term experiments for up to 6 months in a glove box environment. We establish hydrogen production, but being of the same magnitude irrespective whether copper is present or not. Although low, the hydrogen production rate is considerably larger than what would directly correspond to the amount of analysed copper oxidation products. Our analyses encompass the changes to the surface cleaned copper (99·9999%), the water phase and the Duran glass in contact with the water (ppt quality). We have used very sensitive methods (XPS, AES, ICP-MS, XRF) while keeping contamination risks to a minimum. We conclude that the oxidation rate of copper is very low, yielding only parts of a monolayer of Cu2O after 6 months of exposure at 50°C together with an accompanying very low concentration of copper species (4–5 μg L−1) in the water phase.

We have used X-ray absorption (XA) and resonant inelastic X-ray scattering (RIXS) spectroscopies to study a series of copper compounds, namely Cu 2 O , CuO, Cu ( OH ) 2 , CuCl 2 , Cu 2 S , CuSO 4 , malachite ( Cu 2 ( CO 3 ) 2 ( OH ) 2 ) and atacamite ( CuCl 2 · 3 Cu ( OH ) 2 ) . Cu 2p XA spectra provide information about oxidation states. Divalent copper gives a single narrow line due to excitations into the empty 3d state, whereas monovalent copper gives a broad band at higher energy due to transitions to 4s states. Chemical shifts of the main line in the Cu 2 + XA spectra of different compounds are observed but in some cases they are too small to make a clear distinction between the species. It is shown that RIXS at the Cu 2p edge has a great potential to distinguish between the species due to large differences in spectral shapes for the same energy of the incident photon beam. First evidence for the possibility of detecting chemical composition of copper compounds is presented and discussed in details.

The room temperature structures of the tetragonal compounds TlCu 7 S 4 and TlCu 7 Se 4 have been reinvestigated on various fronts, by experiment and theoretical calculations. Neutron powder diffraction data have been analysed by Rietveld profile refinement and Reverse Monte Carlo (RMC) modelling. Both approaches show substantial disorder on the copper site that corresponds to 25% vacancies in the common crystallographic description, and more so in the thiocuprate than in the selenocuprate. Quantum mechanical ab initio calculations were used for an analysis of the interactions between the disordered copper atoms and the host framework. A common space-group description can model only the TlCu 4 S 4 rigid skeleton properly, which is adequately done by the choice of I 4/ m . The remaining copper atoms (three per formula unit) are allowed to move freely in zigzag channels along the c -axis. Both the RMC and ab initio procedures yield copper–copper distances that describe this situation better than a standard crystallographic refinement. The driving force for the disorder with regard to the crystallographic Cu 2 -site atoms appears to be a repulsion between those copper atoms. The degree of disorder is tuned by an interplay between the size of the unit cell and the polarisability of the chalcogen, creating the main difference between the two chalcocuprates in their tendency towards copper rearrangement. Still, the two compounds should be considered isostructural.

A study on the transformation of TlCu 5 Se 3 to the metastable orthorhombic form of TlCu 4 Se 3 upon copper leaching has been conducted using neutron powder diffraction at 10 K and 293 K. The occupancy of the various copper sites in the TlCu 5 Se 3 structure was investigated with Rietveld profile refinement techniques in combination with elemental analysis. The results indicate that mainly one of the three crystallographic copper sites in the parent compound is affected during the extraction process.

The influence of ${\mathrm{Li}}^{+}$ doping, shear under pressure, and irradiation with ${\mathrm{He}}^{+}$ or electrons on the oxygen $2p$-band and valence states of copper ions in CuO was studied using soft-x-ray emission spectroscopy. In the case of irradiation and shear under pressure the transformation of the spectrum shape is explained by the appearance of ${\mathrm{Cu}}_{2}\mathrm{O}.$ The doping with lithium leads to the appearance of copper ions with formal valency of $3+.$ It was also established that the presence of lithium ions prevents ${\mathrm{Cu}}_{2}\mathrm{O}$ phase forming without a dependence on the plastic deformation value. The reasons and possible mechanisms of the $\mathrm{CuO}\ensuremath{\rightarrow}{\mathrm{Cu}}_{2}\mathrm{O}$ transitions in the oxides studied are discussed.

The alleged necessity of changing the space group assignment of TlCu7S4 has been refuted on the basis of room-temperature neutron powder-diffraction data. The structure conforms well to I4m, previously also found for the corresponding ternary selenide. Furthermore, at 255 K a phase transformation occurs to the CsAg7S4 structure type, described in P4n, a crystallographic subgroup of I4m. At 10 K the cell parameters are a = 10.1725(4) A, c = 7.6376(4) A. Contrary to previous findings but in line with expectations, the temperature characteristics of the electrical resistivity of stoichiometric material are those of a semiconductor. However, metallic conductivity occurs after copper depletion owing to valence-band hole formation.

The structure of Li3Cu2O4 was solved from X-ray powder diffraction data and refined from a multiphase specimen using the Rietveld method. The cuprate crystallizes in C2/m with Z = 2. The compound has a small homogeneity range. Typical parameters are a = 9.946(5) A, b = 2.778(2) A, c = 7.260(5) Aand β = 119.10(2)°. The structure may be described as an ordered intergrowth of slabs of Li2CuO2 and hypothetical LiCuO2 of NaCuO2 type. The formula suggests a copper(II, III) mixture, but there is only one crystallographic copper site which implies a more appropriate formulation as Li3+[Cu(II)O2]232 with parallel strands of edge-coupled CuO4 units running along the b axis.

The thallium copper chalcogenides TlCu2S2 and TlCu2Se2, as well as the solid solutions TlCu2SeS and TlCu2 − xFexSe2 (x = 0.5 and 1) have been investigated in the form of powders or single crystals by means of X-ray photoelectron spectroscopy. It is concluded from the absence of Cu 2p shake-up satellites that copper is monovalent, as previously suggested on the basis of electrical transport properties. The metallic character of the copper compounds is due to the presence of valence band holes. Indications of chalcogen ordering were found in TlCu2SeS. On extensive iron substitution the compounds became semiconductors.

The thallium copper chalcogenides TlCu2S2 and TlCu2Se2, as well as the solid solutions TlCu2SeS and TlCu2 − xFexSe2 (x = 0.5 and 1) have been investigated in the form of powders or single crystals by means of X-ray photoelectron spectroscopy. It is concluded from the absence of Cu 2p shake-up satellites that copper is monovalent, as previously suggested on the basis of electrical transport properties. The metallic character of the copper compounds is due to the presence of valence band holes. Indications of chalcogen ordering were found in TlCu2SeS. On extensive iron substitution the compounds became semiconductors.

The crystal structure of copper-deficient TlCu5Se3 has been refined from single-crystal X-ray diffraction data. The previously suggested new structure type was confirmed with agreement factors RF = 0.033 and RwF = 0.035. The symmetry is tetragonal, space group P4 2 mnm (136). For the investigated composition, TlCu4.8Se3, the cell dimensions are a = 12.900 and c = 3.968 A (Z = 4). The structure has features common to other thallium copper chalcogenides such as TlCu3Se2 and TlCu7Se4. Similarities to some multinary alkali metal oxide structures are emphasized.

The structure of TlCu6S4 has been determined from single-crystal X-ray diffraction data, confirming (RF = 0.061, RwF = 0.059) a previous structure hypothesis that the compound is the third member of a structure series TlCu2nSn+1. The compound is tetragonal (space group I4/mmm, no. 139; Z = 2) with the cell parameters a = 3.9465 A , c = 24.230 A for nearly stoichiometric material. The investigated crystal was copper deficient, corresponding to the formula TlCu5.5S4 and to the cell parameters a = 3.9357 A , c = 24.183 A . Like the previous members of the series, this compound has metallic conduction owing to a high concentration of valence band holes. All the members of the series are layer structures with tetragonal symmetry, derived from anti-fluorite-type Cu2S with thallium layers interfoiling slabs with copper in tetrahedral voids of the sulphur lattice.

The structure of TlCu6S4 has been determined from single-crystal X-ray diffraction data, confirming (RF = 0.061, RwF = 0.059) a previous structure hypothesis that the compound is the third member of a structure series TlCu2nSn+1. The compound is tetragonal (space group I4/mmm, no. 139; Z = 2) with the cell parameters a = 3.9465 A , c = 24.230 A for nearly stoichiometric material. The investigated crystal was copper deficient, corresponding to the formula TlCu5.5S4 and to the cell parameters a = 3.9357 A , c = 24.183 A . Like the previous members of the series, this compound has metallic conduction owing to a high concentration of valence band holes. All the members of the series are layer structures with tetragonal symmetry, derived from anti-fluorite-type Cu2S with thallium layers interfoiling slabs with copper in tetrahedral voids of the sulphur lattice.

In the p-type metal TlCu2Se2, monovalent copper may be substituted by various metals with higher valence. The physical properties of the system TlCu2−xFexSe2 have been studied as a function of the composition in some detail, with emphasis on the range 0

Beim Versuch, einen fur die Rontgen-Strukturverfeinerung geeigneten TaNiP-Kristall auszulesen, wird die neue Phosphidphase (I) mit tetragonaler Symmetrie entdeckt.

The structure of NH4Cu7−xS4 has been investigated using X-ray single crystal diffraction at varying temperatures. The room temperature structure is best described as a tetragonal crystalline framework with channels incorporating some of the copper atoms in a disordered, almost amorphous, manner. The crystallographic description based primarily on the framework renders the space group I4/m and a unit cell with a=10.2695(5) A and c=3.8094(3) A. Upon cooling below 270 K, the copper atoms in the channels start to order. To begin with, the compound adopts the CsAg7S4 structure type with the unit-cell parameters a=10.289(1) A and c=7.704(1) A. Upon further cooling, incommensurate orderings occur, in accordance with the fact that a copper deficient sample was used in the investigation (x≈0.16).

The structure of LiCu2O2 was solved using two sets of X-ray diffraction twin-crystal data. Extended twinning creates virtual tetragonal symmetry. The compound crystallizes in Pnma (62) with unit-cell parameters a = 5.72 angstrom, b = 2.86 angstrom and c = 12.4 angstrom with a certain homogeneity range. The structure consists of LiCu(II)O2 layers interleaved by layers of Cu(I) connected to oxygen in an almost linear coordination. Lithium and copper(II) have five oxygen neighbours in pyramidal arrangements that run as parallel bands through edge connections. Electron diffraction was used for characterizing the twinning.