Search

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 solid state transformation of monoclinic TlCu 3 Se 2 into tetragonal TlCu 2 Se 2 by oxidative copper leaching in concentrated ammonia solution has been studied in situ by the use of synchrotron radiation. The diffraction patterns of parent and daughter phase are both sharp, indicating a strong topotactic relationship between them that effectuates a rapid change by “chimie douce” performed at +19 °C. The transformation rate is strongly connected to the access of oxygen from the surrounding air. The transformation was followed in a real-time mode, being almost complete after 2.5 h with 1 h incubation due to low oxygen content, as shown from refining the diffraction patterns by Rietveld profile technique.

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.

The magnetic layer structure of TlCo2Se2−xSx has been thoroughly re-investigated with neutron powder diffraction. The cobalt magnetic moments are ferromagnetically arranged within the layers, but the interlayer coupling differs profoundly with varying composition (x): the spins in TlCo2Se2 form a helix along the c-axis with a turning-angle of ∼119° at 1.4 K. This kind of helical structure prevails for 0≤x≤1.5 with a gradual decrease of the angle with increasing sulphur content, down to 34°, showing an almost linear relationship with the interlayer distance of Co–Co. For x≥1.75 the interlayer coupling changes to ferromagnetic. Unexpectedly, two helices were found to coexist at x=0.5 and x=1.0. The interaction between adjacent cobalt layers is there characterized by an incommensurate angle (106°, resp., 73°) together with a commensurate angle of 90°. The magnetic structures have been refined as two magnetic phases, each having a characteristic wave vector. A tentative model where the symmetry of the structure and the interlayer distance compete is considered for explaining the simultaneous occurrence of the two kinds of diffraction profile satellites.

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.

Objective. Pulmonary arterial hypertension (PAH) associated with congenital heart defect (CHD), and especially Eisenmenger syndrome, is associated with impaired exercise tolerance and reduced quality of life. In this study, we describe medium-term follow-up of adult patients with PAH associated with CHD, treated in a single center with different types of advanced medication. Design. The treatment and clinical course of 15 patients (11 female, median age 53, range 28–74 years) with PAH associated with CHD is retrospectively described. Data on patient characteristics, exercise test, right-heart catheterization, and type of advanced therapy were collected from medical files. Advanced medical therapy consisted of either intravenous prostacyclin, or endothelin receptor antagonists, or phosphodiesterase-5-inhibitors. Additional therapy was started in case of persistent clinical deterioration or insufficient improvement with monotherapy. Results. All patients (10 patients with Eisenmenger syndrome, 5 patients with a closed defect and PAH) were exposed to different durations of advanced medication. Median period of treatment was 2.5 (range 0.7–6.3) years. Atrial septal defect, type secundum, was the most frequent underlying diagnosis (n = 10). Most patients (n = 9) received a combination of advanced medical therapy. Six-minute walk distance (6-MWD) remained unchanged with an increase of 44 ± 78 m (P = 0.2) and 41 ± 80 m (P = 0.3) compared with baseline after respectively 1 and 2 years of treatment. Younger age was associated with better performance (β = −7 m per year, P

Various solid solutions TlCo 2− x Me x Se 2 (Me=Fe, Ni and Cu) have been investigated by neutron powder diffraction, supplemented by magnetometry. The incommensurate spin-helix running along the c -axis in tetragonal TlCo 2 Se 2 prevails for low concentrations of copper and iron but changes pitch. In the copper case, only cobalt carries a magnetic moment. On nickel substitution, however, collinear antiferromagnetic coupling between the ferromagnetic layers occurs. The magnetic moment distribution between the two transition metals in the solid solution TlCo 2− x Ni x Se 2 was tentatively probed with first principle calculations on fictive ordered TlCoNiSe 2 , modelled by two types of superstructures. Also the ternary mother compounds, Pauli paramagnetic TlNi 2 Se 2 and antiferromagnetic TlCo 2 Se 2 , were investigated with the same LMTO method.

TlCu2-xFexSe2 is a p-type metal for x < 0.5 which crystallizes in a body-centred tetragonal structure. The metal atoms are situated in ab-planes, similar to 7 angstrom apart, while the metal - metal distance within the plane is similar to 2.75 angstrom. Due to the large difference in cation distances, the solid solutions show magnetic properties of mainly two-dimensional character. The SQUID measurements performed for x = 0.27 give the c-axis as the easy axis of magnetization, but also show clear hysteresis effects at 10 K, indicating a partly ferromagnetic coupling. The magnetic ordering temperature T-c is 55( 5) K as found from both SQUID and Mossbauer spectra. At T << Tc the magnetic hyperfine fields are distributed with a maximum at about 30 T, which are compared to the measured magnetic moment per iron atom, which is 0.97 mu(B)/Fe as found from SQUID measurements. The experimental results are compared to results using other methods on isostructural Tl selenides.

The system TlCo2Se2-xSx has been thoroughly investigated by neutron powder diffraction and SQUID magnetometry. TlCo2Se2-xSx is a layered tetragonal structure containing atomic cobalt layers separat ...

The electronic structure of TlCo2Se2 has been investigated by means of band structure calculations and x-ray photoelectron and emission spectroscopy (XPS and XES). The formation of the valence band is described in connection with calculations of partial densities of states of the valence band and Co Lα,β x-ray emission () aligned to the binding energy scale. The experimental results are in agreement with the calculated distribution of Co 3d states, which lie close to the Fermi level. The effect of Co–Se bonding is seen as satellite structures in the XPS Co 2p signals. Thermoelectric and Hall effect data as well as resistivity measurements show that TlCo2Se2 is metallic with electron holes as charge carriers with broadband mobility characteristics. The observed anisotropy of the resistivity in the ab plane and along c remains constant as a function of temperature, i.e. without signs of the magnetic ordering that occurs (TN~85 K). The results of local spin density functional calculations show ferromagnetic coupling within the cobalt plane as a result of direct magnetic interactions between the magnetic moments.

At isovalent substitution of Se for S, the layered chalcogenides TlCo 2 Se 2− x S x (0⩽ x ⩽2) exhibit a change of magnetic order type, from an antiferromagnetic helix at low S content to a ferromagnet at high S content. The effective magnetic moments p eff ∼2 μ B per Co, as estimated from the magnetic susceptibility at high temperatures, significantly exceed what would be the result of the Co magnetic moments μ sat ∼0.5 μ B in both the ferromagnetic and antiferromagnetic phases. This signifies the crucial role of longitudinal spin fluctuations in the magnetic behaviour of these conducting compounds. The spin fluctuations reveal themselves also in specific heat measurements, leading to a diminution of the expected anomalies at the Curie/Neel temperatures and to an excess of heat capacity at high temperatures as compared to phonon contributions.

An extensive investigation of the ferromagnetic compound TlCo2S2 has resulted in new information on the electronic and magnetic structure. Electronic structure calculations showed that magnetic ord ...

The quasi two-dimensional antiferromagnetic compound TlCo2Se2 has been studied by 57Fe Mossbauer spectroscopy. Small single crystals have been made with 2% Fe doping. The Mossbauer spectrum, developed below the Neel temperature of 85 K, reveals a distribution of magnetic hyperfine fields (MHF). The fit is reasonably good if we suppose a connection between the values and mutual orientation of the EFG and MHF. That allows us to suggest the existence of a modulation in the helical magnetic structure, discovered earlier by neutron diffraction.

The structural and magnetic properties of TlCo 2− x Cu x Se 2 have been investigated experimentally. The antiferromagnetic coupling already found in TlCo 2 Se 2 prevails on copper substitution but is weakened. For high copper contents, x >1.3, Pauli paramagnetism occurs. The susceptibility measurements point towards a picture of ferromagnetic Co moments aligned perpendicular to the c -axis. The cobalt atoms are confined to sheets, between which there is antiferromagnetic coupling. Structurally we observe a change in symmetry from I-centred tetragonal ( Z =2) to face-centred orthorhombic ( Z =4) in the range 0 x 2 Se 2 has been re-investigated by neutron powder diffraction. Below T N ∼80 K, it is characterised by a helimagnetic arrangement of spins confined to the Co sheets, the helix running along the c -axis. The moments lie in the (002) planes with a helical turn angle of about 121° between two adjacent Co layers. At 10 K, the moment refined to 0.46 μ B /Co atom.

Purpose: Budesonide and flunisolide anhydrate were crystallized using the solution enhanced dispersion by supercritical fluids (SEDS) technique. The aim was to investigate the possibility of preparing different pure polymorphs.

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.

Cu/Co ordering in TlCo2−xCuxSe2, (x∼1) has been investigated using electron and X-ray powder diffraction. The average structure of the x=1 compound can be indexed on an F-centered orthorhombic cell, a=5.5518(6) A, b=5.4755(5) A, and c=13.7387(17) A. Additional weak satellite reflections characterized by the primary modulation wave vector qi∼0.184a* and indicative of an incommensurate modulated structure are revealed by electron diffraction. Characteristic extinction conditions in conjunction with mmm Laue symmetry and known crystal chemical constraints imply a (3+1)-dimensional superspace group symmetry of Fmmm(α01)00s. The incommensurate modulation is attributed to occupational ordering of the two transition metal atoms and associated structural relaxation. The real space interpretation of the Cu/Co ordering pattern is that copper and cobalt atoms form separate layers in the structure at z= 1 4 and 3 4 , respectively. These layers are periodically interchanged as one moves along the x direction. Two periods of this square-wave-like modulation is close to 11a in length but is non-rational compared with the average structure.

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 electronic structure of LiCu${}_{2}$O${}_{2}$ was studied using x-ray emission (Cu ${L}_{\ensuremath{\alpha}},$ O ${K}_{\ensuremath{\alpha}})$ and photoelectron spectroscopy (valence band and core levels) as well as band-structure calculations in terms of local spin-density approximation (LSDA) and LSDA+$U$ approaches. According to the x-ray-emission and photoelectron spectra the valence states of the Cu atoms are found to be mixed, i.e., 2+ and 1+. The LSDA calculations are contradictory to the experimental data and cannot reproduce the band gap and magnetic properties of ${\mathrm{LiCu}}_{2}{\mathrm{O}}_{2}$. The LSDA+$U$ calculations describe the insulator and antiferromagnetic properties much better but the overestimation of the screened Coulomb parameter $U$ leads to a binding-energy shift of the Cu${}^{\mathrm{II}}$ $3d$ states and this distorts the proper modeling of the valence-band structure. The magnetic structure of LiCu${}_{2}$O${}_{2}$ is discussed, taking our LSDA+$U$ band-structure calculations into account.

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.

An orthorhombic modification of TlCu4Se3 was synthesised at room temperature by oxidative copper extraction from TlCu5Se3. It crystallises in a new structure type, space group Pnnm, with the cell parameters a = 12.4306(2) A, b = 12.7997(2) A, c = 3.93516(6) A. The structure is closely related to the tetragonal structure of the parent compound. For the structure solution direct methods were used on single-phase Guinier-Hagg X-ray powder film data. In the refining stage, the Rietveld method was applied on powder diffractometer data. After being heated above 670 K, this orthorhombic form completely transforms to the tetragonal modification. Both are metallic conductors.

The mechanism of the TlCu3S2/TlCu2S2 phase transformation has been studied experimentally by neutron diffraction and theoretically by three-dimensional Hueckel band calculations. Experiments show t ...

LiCuO2 was synthesized at room temperature by delithiation of Li2CuO2 using bromine in acetonitrile. The product shows broad diffraction lines which were analysed by the Rietveld refinement technique on X-ray and neutron powder data. The phase conforms to the NaCuO2 structure type

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.

In the Li-Cu-O system two new ternary phases have been found, tentatively described by the stoichiometries LiCu3O3 and LiCu2O2, and both containing Cu1 and Cu11. They exhibit p-type “hopping” conduction owing to localized charge carriers. Their powder patterns are successfully indexed on high-symmetry cells where the dimensions depend on a slightly variable stoichiometry. LiCu3O3 is tetragonal with a = 2.815 (·√2) A and c = 8.88 A . LiCu2O2 is orthorhombic with a = 5.72 A , b = 2.86 A and c = 12.4 A . Li3Cu2O4, containing Cu11 and Cu111, is indexed on a C-centred monoclinic cell: a = 9.958 A , b = 2.777, c = 7.281 A and β = 118.77 ° . The solubility of lithium in CuO is maximally Li0.06Cu0.94O for supersaturation at 1100 K. The equilibrium solubility limit is about Li0.02Cu0.98O, for which the solid solution is still semiconducting. The temperature dependence of the magnetic susceptibility is similar to that of pure CuO but TN is considerably lower.

LiCuO2 was synthesized at room temperature by delithiation of Li2CuO2 using bromine in acetonitrile. The product shows broad diffraction lines which were analysed by the Rietveld refinement technique on X-ray and neutron powder data. The phase conforms to the NaCuO2 structure type

In its inherent ability to discern light elements in a heavy-atom matrix, neutron powder diffraction has been used at room temperature to confirm structure hypotheses of LiCu 2 O 2 ( R I = 2.18%; R P = 4.21%) and LiCu 3 O 3 ( R I = 2.19%; R rmP = 5.45%), inferred from previous X-ray diffraction studies. LiCu 2 O 2 is orthorhombic, described by the space group Pnma ( Z =4), as suggested from a structure determination from twin-crystal data. The cell parameters found were a=5.7260(4) A , b=2.8587(2) A and c=12.4137(7) A . The apparent tetragonal symmetry independently advocated must be definitively discarded as an artifact from twinning. LiCu 3 O 3 was successfully refined on a tetragonal cell-with a=2.8142(1) A and c=8.8956(5) A -in P4/mmm (Z=1) using a single-crystal model. The data were insufficient to test any superstructure model.

Previously, chemical oxidation of TlCu 3 X 2 (X= S,Se) as a powder immersed in ammonia solution effectuated a phase transformation into the p -metal TlCu 2 X 2 . In order to explore whether the small grain size and intimate contact with the liquid phase were imperative, we introduce an electrochemical method with the starting phase as a polished rotating electrode. Moreover, the inherent possibility of changing the polarity is a unique way to enable the reverse transformation. Bulk phase transformations are possible for both directions. The microstructures of polished electrode surfaces indicate that processes within the solid rather than in the interface with the electrolyte are important. The slower and less efficient reduction process may be explained from topotactic symmetry considerations. The developed microstructures of the electrode surfaces support orientational topotaxy.

The electronic structure of MnO has been investigated using high-energy (x-ray photoelectron and bremsstrahlung-isochromat) spectroscopies. An experimental gap of 3.9 eV is found. By comparing the experimental results to a configuration-interaction cluster model, values for the different parameters in a model Hamiltonian are found [U=8.5 eV, DELTA = 8.8 eV, and (pd-sigma) = 1.3 eV]. These parameter values place MnO in the intermediate region of the Zaanen-Sawatzky-Allen phase diagram. By using the same parameters, the d-d forbidden optical-absorption energies can be calculated, and good agreement with experiment is found.

TlFe 2- x Se 2 compounds with x values around 0.4 have been characterized by X-ray diffraction and examined by Mossbauer spectroscopy. The iron vacancies are ordered to some extent, but a ThCr 2 Si 2 type subcell structure can be recognized. Antiferromagnetic ordering occurs below a Neel temperature which is strongly dependent on x . The transition seems to be of first order. In contrast to a previous study on a single crystal, these specimens show less pronounced vacancy ordering and a higher extrapolated Neel temperature, which may be explained by a larger number of iron nearest neighbours. The magnetic transition regions are broad, indicating weak interactions between the layers containing iron. A difference in the isomer shifts for the coexisting para- and antiferromagnetic phases was observed, tentatively explained by a difference in the conduction electron density owing to iron vacancies. The electric quadrupole interaction has a T 3 2 dependence in the paramagnetic phase.

The structure of TlCu7Se4 (synthetic crookesite) has been refined from X-ray powder data using the Rietveld technique. The compound is isostructural with NH4Cu7S4 and TlCu7S4, although successful r ...

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.

TlFe2−x Se2 compounds withx from 0.36 to 0.40 have been examined with Mossbauer spectroscopy. The compounds order antiferromagnetically with broad magnetic transition regions whose width increases with decreasing Fe content. The Neel temperature decreases with x and the temperature variation of the magnetic hyperfine field indicates that the transition is of first order. In samples without vacancy ordering the Fe nuclei experience a different temperature variation of the hyperfine field than in compounds with ordered vacancies.

The crystal structure of TlCu3Se2 has been refined (RF = 0.050, RwF = 0.045; 349 reflections, 37 parameters) from X-ray single-crystal diffraction data. The compound is of the CsAg3S2 type, space group C2/m, with the cell parameters a = 15.2128(7) A , b = 4.0115(2) A , c = 8.3944(4) A and β = 111.700(4)°. Comparison is made with the Tl5Cu14Se10 structure that can be derived from a TlCu3Se2 arrangement by a modified stacking sequence of common slabs, accommodating the slight copper deficiency.

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 magnetic properties of two compositions of random solutions in the TlCu2-xFexSe2 system with x = 0.2 and 0.45 have been investigated by superconducting quantum interference device magnetometry. The crystal structure is of a layer type and ordering due to the iron atoms occurs at low temperatures, with T-c = 85 K for x = 0.2 and T-c = 130 K for x = 0.45. The samples were highly textured crystals and the magnetic moments of both compositions were found to align along the c axis of the structure. The saturation moments were found to be 1.5 mu(B)/Fe x = 0.2 and 0.66 mu(B)/Fe for x = 0.45. (c) 2005 American Institute of Physics.

Thin metal films have found their use in many magnetic devices. They form pseudo two-dimensional systems, where the mechanisms for the magnetic interactions between the layers are not completely understood. Layered crystal structures have an advantage over such artificial systems, since the layers can be strictly mono-atomic without any unwanted admixture. In this study, some model systems of layered magnetic crystal structures and their solid solutions have been investigated by x-ray and neutron diffraction, Mossbauer and electron spectroscopy, heat-capacity and magnetic measurements, and first-principle electronic structure calculations, with the goal of deepening our understanding through controlled chemical synthesis.The compounds TlCo2S2, TlCo2Se2 and their solid solution TlCo2Se2-xSx, all containing well separated cobalt atom sheets, order with the moments ferromagnetically aligned within the sheets. In TlCo2S2, the net result is ferromagnetism, while TlCo2Se2 exhibits antiferromagnetism. The inter-layer distance is crucial for the long-range coupling, and it was varied systematically through Se-S substitution. The incommensurate helical magnetic structure found for TlCo2Se2 (x = 0) prevails in the composition range 0 ≤ x ≤ 1.5 but the pitch of the helix changes. The accompanying reduction in inter-layer distance on sulphur substitution varies almost linearly with the coupling angle of the helix. An additional competing commensurate helix (90°) appears in the medium composition range (found for x = 0.5 and 1.0).The systems TlCo2-xMexSe2 show helical magnetic ordering for Me = Fe or Cu, while a collinear antiferromagnetic structure occurs for Me = Ni. Magnetic order is created by iron substitution for copper in the Pauli paramagnetic TlCu2Se2, but now with the moments perpendicular to the metal sheets.TlCrTe2 forms a quite different crystal structure, with intra-layer ferromagnetic alignment and net collinear antiferromagnetism. In contrast to the other phases, the values of the moments conform well to a localised model for Cr3+.