Synchrotron Powder Diffraction Research Articles

Unravelling the crystal structure of Nd5.8WO12-δ and Nd5.7W0.75Mo0.25O12-δ mixed ionic electronic conductors.

Mixed ionic electronic conducting ceramics Nd6-y WO12-δ (δ is the oxygen deficiency) provide excellent stability in harsh environments containing strongly reactive gases such as CO2, CO, H2, H2O or H2S. Due to this chemical stability, they are promising and cost-efficient candidate materials for gas separation, catalytic membrane reactors and protonic ceramic fuel cell technologies. As in La6-y WO12-δ, the ionic/electronic transport mechanism in Nd6-y WO12-δ is expected to be largely controlled by the crystal structure, the conclusive determination of which is still lacking. This work presents a crystallographic study of Nd5.8WO12-δ and molybdenum-substituted Nd5.7W0.75Mo0.25O12-δ prepared by the citrate complexation route. High-resolution synchrotron and neutron powder diffraction data were used in combined Rietveld refinements to unravel the crystal structure of Nd5.8WO12-δ and Nd5.7W0.75Mo0.25O12-δ. Both investigated samples crystallize in a defect fluorite crystal structure with space group Fm 3 m and doubled unit-cell parameter due to cation ordering. Mo replaces W at both Wyckoff sites 4a and 48h and is evenly distributed, in contrast with La6-y WO12-δ. X-ray absorption spectroscopy as a function of partial pressure pO2 in the near-edge regions excludes oxidation state changes of Nd (Nd3+) and W (W6+) in reducing conditions: the enhanced hydrogen permeation, i.e. ambipolar conduction, observed in Mo-substituted Nd6-y WO12-δ is therefore explained by the higher Mo reducibility and the creation of additional - disordered - oxygen vacancies.

Structural study of decrespignyite-(Y), a complex yttrium rare earth copper carbonate chloride, by three-dimensional electron and synchrotron powder diffraction

Abstract. The crystal structure of the mineral decrespignyite-(Y) from the Paratoo copper mine (South Australia) has been obtained by applying δ recycling direct methods to 3D electron diffraction (ED) data followed by Rietveld refinements of synchrotron data. The unit cell is a= 8.5462(2), c= 22.731(2) Å and V= 1437.8(2) Å3, and the chemical formula for Z=1 is (Y10.35REE1.43Ca0.52Cu5.31)Σ17.61(CO3)14Cl2.21(OH)16.79⋅18.35H2O (REE: rare earth elements). The ED data are compatible with the trigonal P3‾m1 space group (no. 164) used for the structure solution (due to the disorder affecting part of the structure, the possibility of a monoclinic unit cell cannot completely be ruled out). The structure shows metal layers perpendicular to [001], with six independent positions for Y, REE and Cu (sites M1 to M4 are full, and sites M5 and M6 are partially vacant), and two other sites, Cu1 and Cu2, partially occupied by Cu. One characteristic of decrespignyite is the existence of hexanuclear (octahedral) oxo-hydroxo yttrium clusters [Y6(μ6-O)(μ3-OH)8O24] (site M1) with the 24 bridging O atoms belonging to two sets of symmetry-independent (CO3)2− ions, with the first set (2×) along a ternary axis giving rise to a layer of hexanuclear clusters and the second set (6×) tilted and connecting the hexanuclear clusters with hetero-tetranuclear ones hosting Cu, Y and REE (M2 and M3 sites). The rest of the crystal structure consists of two consecutive M3 + M4 layers containing the partially occupied M5, M6, and Cu2 sites and additional carbonate anions in between. The resulting structure model is compatible with the chemical analysis of the type material which is poorer in Cu and richer in (REE, Y) than the above-described material.

High resolution structural refinement and band gap characterization of the defect chalcopyrites CuIn5Te8, AgIn5Te8 and AuIn5Te8

The AIn5Te8 compounds (A ​= ​Cu, Ag, Au), charge balanced defect chalcopyrites, are characterized. Synchrotron powder diffraction shows that the Cu and Ag analogs are tetragonal to high precision at room temperature, with classic 158 (I-III5-VI8) defect chalcopyrite structures in space group I4¯2m. These materials display ordered vacancies but disordered cations. The degree of cation intermixing is more significant in the Cu case than in the Ag case. In contrast, AuIn5Te8, a previously unreported 158 defect chalcopyrite, exhibits a tetragonal P4¯2c structure with disordered vacancies and cations, displaying poorer crystallinity than the other two materials. The direct optical band gaps (Eg), determined from UV–vis absorption measurements, are estimated to be 0.94, 0.99, and 0.77 ​eV, respectively. Comparison to the corresponding sulfides and selenides for 158 and standard 112 (I-III-VI2) type chalcopyrites is reported where the data are available.

Ferrimagnetic Ordering and Anomalous Stoichiometry Observed for the Cubic, Extended 3D Prussian Blue Analogues (NEt3 Me)2 MnII 5 (CN)12 and (NEt2 Me2 )2 MnII 5 (CN)12 : A Cation-Adaptive Structure.

The reactions of MnII (O2 CCH3 )2 with NEt3 Me+ CN- and NEt2 Me2 + CN- form (NEt3 Me)2 MnII 5 (CN)12 (1) and (NEt2 Me2 )2 MnII 5 (CN)12 (2), respectively. Structure model-building and Rietveld refinement of high-resolution synchrotron powder diffraction data revealed a cubic [a=24.0093 Å (1), 23.8804 Å (2)] 3D extended structural motif with adjacent tetrahedral and octahedral MnII sites in a 3:2 ratio. Each tetrahedral MnII site is surrounded by four low-spin octahedral MnII sites, and each octahedral MnII site is surrounded by six high-spin tetrahedral MnII sites; adjacent sites are antiferromagnetically coupled in 3D. Compensation does not occur, and magnetic ordering as a ferrimagnet is observed at Tc =13 K for 2 based on the temperature at which remnant magnetization, Mr (T)→0. The hysteresis has an unusual constricted shape with inflection points around 50 and 1.2 kOe with a 5 K coercivity of 16 Oe and remnant magnetization, Mr , of 2050 emuOe mol-1 . The unusual structure and stoichiometry are attributed to the very ionic nature of the high-spin N-bonded MnII ion, which enables the maximization of the attractive van der Waals interactions through minimization of void space via a reduced ∠ MnNC. This results in an additional example of the Ax MnII y (CN)x+2y (x=0, y=1; x=1, y=3; x=2, y=1; x=2, y=2; x=2, y=3; x=3, y=5; and x=4, y=1) family of compounds possessing an unprecedented stoichiometry and lattice motif that are cation adaptive structured materials.

Belite hydration at high temperature and pressure by in situ synchrotron powder diffraction

Portland cements are currently used as Oil‐Well‐Cements for the sheath between the metal casing and the borehole. At high pressures and temperatures, the resulting C–S–H gel(s) is partly unstable and it can react to give different crystalline phases and changing microstructure which increases porosity. It is known that the addition of silica-rich materials to Portland cements, used to decrease the overall Ca/Si molar ratio, avoids/minimises the early strength retrogression experienced by neat cement slurries. Alternatively, belite-rich cement could be used but belite reactivity in these conditions is largely unexplored. Here, belite-rich mixtures have been quantitatively studied at 180 bars and of 160 °C by in situ synchrotron powder diffraction using a tailored-designed spinning capillary cell. For model alite/belite mixtures, alite strongly accelerates belite hydration in these conditions. At 10 h of hydration, β-C2S shows a reaction degree of 30 and 80% for 20 wt%C3S-80 wt%C2S and 50 wt%C3S-50 wt%C2S mixtures, respectively. Furthermore, the 50 wt%C3S mixture hydrates yielding significant amounts of Jaffeite and α-C2SH and the 20 wt%C3S mixture gave no Jaffeite and much lower amount of α-C2SH. Finally, a belite cement has also been hydrated in these conditions and the reaction degree of belite was 50% at 10 h. The hydration of this cement did not yield Jaffeite neither α-C2SH in the studied experimental conditions.

New examples of non-cooperative octahedral tilting in a double perovskite: phase transitions in K3GaF6.

The crystal structures of three polymorphs of K3GaF6 and the transition temperatures between these phases are reported for the first time. Synchrotron powder diffraction data clearly show that at 300 K α-K3GaF6 crystallizes in space group I41/a with lattice parameters of a = 19.1124 (3) Å, c = 34.4165 (6) Å, and Z = 80. The structure is based on the double perovskite but with two fifths of the GaF6 octahedra rotated by ∼45°. This phase remains stable until ∼460 K, above which it undergoes a transition to I4/m with lattice parameters of a = 13.6088 (4) Å, c = 8.6764 (3) Å, and Z = 10 at 485 K. β-K3GaF6 has a similar structure but with only one fifth of the GaF6 rotated by ∼45°. Above ∼510 K, the cubic Fm3m δ-K3GaF6 structure is stabilized, with a lattice parameter of a = 8.6649 (1) Å at 550 K. The F atoms have highly anisotropic displacement parameters which suggest dynamic octahedral tilting is occurring. This work expands the fairly small group of double perovskite compounds which display non-cooperative patterns of octahedral tilting.

Location of 6-azonia-spiro- [5,5]-undecane molecules in ZSM-12 using X-ray synchrotron powder diffraction data

High-silica ZSM-12 (MTW topology), synthesized with 6-azonia-spiro- (Rimer, 2018; Rimer, 2018) [5,5]-undecane as structure directing agent (SDA), was carefully characterized by using X-ray synchrotron powder diffraction. The structure refinement led to a monoclinic unit cell (space group Cc, Z = 4, a = 25.0814(13) Å, b = 15.0987(8) Å, c = 24.4419(17) Å, β = 107.844(6), V = 8810.8(8) Å3) with a three times enlargement of the unit cell along the b axis with respect to the calcined starting ZSM-12 (space group C2/c, Z = 1, a = 24.8633(3) Å, b = 5.01238(7) Å, c = 24.3275(7) Å, β = 107.7215(6)°). The SDAs conformation and position in the framework structure did not maintain the twofold axes coinciding with the crystallographic twofold axis thus changing the space group symmetry from C2/c to Cc. The structure refinement gave an extraframework content 6.13 SDA molecules per unit cell (corresponding to ~9.0 wt%) in good agreement with the weight loss given by the thermogravimetric analysis. The refined bond distances revealed the occurrence of non-bonding interactions of both azonia molecules with the MTW pore wall. AZO-1 and AZO-2 molecules are H-bonded between them thus forming clusters aligned along the b axis. This information is crucial to tailor the physicochemical properties of zeolites as well as to address their hydrophobicity, pore dimensions and cavities thus optimizing the selectivity of zeolite catalysts.

High-Temperature Evolution of the Incommensurate Composite Crystal Ca0.83CuO2

The crystal structure of the composite crystal Ca0.83CuO2 was investigated by synchrotron powder diffraction at high temperature. The incommensurate modulated structure was firstly analyzed at room temperature (RT) and successfully solved by adopting the (3D + 1)-dimensional symmetry P21/m(α0γ)0s. The composite crystal is featured by a non-uniform distribution of Ca ions occupying octahedral sites formed by the spatial arrangement by the infinite 1D CuO2 chains. By approaching 500 K, Ca0.83CuO2 undergoes a structural rearrangement ruled by the shrinking of the Ca interatomic distances. The high-temperature crystalline phase is characterized by a different incommensurate periodicity requiring the recombination of the Ca/CuO2 balance featuring the composite intergrowth of the two almost independent sub-structures. We ascertain that the new crystalline form is stable up to 950 K near to the limit of the thermal decomposition.

In-Depth Study of Li4Ti5O12 Performing beyond Conventional Operating Conditions.

Lithium-ion batteries (LIBs) are nowadays widely used in many energy storage devices, which have certain requirements on size, weight, and performance. State-of-the-art LIBs operate very reliably and with good performance under restricted and controlled conditions but lack in efficiency and safety when these conditions are exceeded. In this work, the influence of outranging conditions in terms of charging rate and operating temperature on electrochemical characteristics was studied on the example of lithium titanate (Li4Ti5O12, LTO) electrodes. Structural processes in the electrode, cycled with ultrafast charge and discharge, were evaluated by operando synchrotron powder diffraction and ex situ X-ray absorption spectroscopy. On the basis of the Rietveld refinement, it was shown that the electrochemical storage mechanism is based on the Li-intercalation process at least up to current rates of 5C, meaning full battery charge within 12 min. For applications at temperatures between -30 and 60 °C, four carbonate-based electrolyte systems with different additives were tested for cycling performance in half-cells with LTO and metallic lithium as electrodes. It was shown that the addition of 30 wt % [PYR14][PF6] to the conventional LP30 electrolyte, usually used in LIBs, significantly decreases its melting point, which enables the successful low-temperature application at least down to -30 °C, in contrast to LP30, which freezes below -10 °C, making battery operation impossible. Moreover, at elevated temperatures up to 60 °C, batteries with the LP30/[PYR14][PF6] electrolyte exhibit stable long-term cycling behavior very close to LP30. Our findings provide a guideline for the application of LTO in LIBs beyond conventional conditions and show how to overcome limitations by designing appropriate electrolytes.

Crystal structure and X-ray absorption spectroscopy of trimethylarsine oxide dihydrate, (CH3)3AsO⋅2H2O

The crystal structure of trimethylarsine oxide dihydrate, (CH3)3AsO⋅2H2O, (TMAO dihydrate) has been solved using parallel tempering with the FOX software package and refined using synchrotron powder diffraction data obtained from beamline 08B1-1 at the Canadian Light Source. Rietveld refinement, performed with the software package GSASII, yielded orthorhombic lattice parameters of a = 13.3937(4) Å, b = 9.53025(30) Å, and c = 11.5951(3) Å (Z = 8, space group Pbca). The Rietveld refined structure was compared with density functional theory calculations performed with VASP and shows reasonable agreement. Arsenic K-edge X-ray absorption spectroscopy analysis also revealed additional information on the electronic structure of the arsenic atom within the TMAO dihydrate structure.

Selective laser melting of thermal pre-treated metal oxide doped aluminum oxide granules

The influence of powder bed density on the final density and microstructure of aluminum oxide parts manufactured by direct selective laser melting has been studied. Iron oxide and manganese oxide nanoparticles were used to improve laser absorption by over eighty percent. To achieve such values, flowable doped alumina granules were prepared by spray drying. Thermal treatment of the granules at 1600 ​°C and consecutive mixing with coarse alumina allowed improvement of the tapped powder densities, reaching a maximum value of 56.4% of the theoretical density. This led to laser processed parts with densities up to 98.6% measured by tomographic microscopy. Measurements with an integrating sphere and an UV-VIS-NIR spectrophotometer employing Kubelka-Munk theory show the decrease of absorptance caused by thermal pre-treatment. 3D mapping by X-ray μ-beam fluorescence contrast tomography and high resolution synchrotron powder diffraction provide information about the variation of dopant distribution and composition within the granules.

Ni–Cr–Al Alloy for neutron scattering at high pressures

ABSTRACTHigh-pressure devices used in neutron scattering require materials with high strength, low neutron attenuation, and no activation. They should also be non-magnetic. Only very few materials fulfil these criteria. Here, it is reported on the manufacture and properties of the Ni–Cr–Al alloy (57.0 wt-% Ni, 40.0 wt-% Cr, and 3.0 wt-% Al). The casting and heat treatment to obtain the material with the optimal yield strength are described in detail. Synchrotron powder diffraction reveals that phases of the Ni2Cr, Cr, and Ni3Al types are present. Aging has no significant effect on their lattice parameters and volume fractions. The alloy has no magnetic order down to at least 1.9 K as evidenced by magnetic measurements and diffraction with polarised neutrons.This paper is part of a Thematic Issue on The Crystallographic Aspects of Metallic Alloys.

NaSeC2H: A Crystalline Compound with Disordered –SeC2H Anions

By reaction of NaC2H with elemental selenium (grey or red) in liquid ammonia a crystalline brownish powder of NaSeC2H was obtained. The existence of the new –SeC2H anion – recently discovered in AISeC2H (AI = K, Rb, Cs) – was confirmed by IR spectra showing the expected C≡C, C–H, and C–Se vibrations. A synchrotron powder diffraction pattern (SNBL, ESRF/Grenoble) was indexed in a cubic unit cell with a = 7.044 Å. Analysis of the data led to a pyrite‐type structure (Pa3, Z = 4) with a static orientational disorder of the –SeC2H anions over two positions. No phase transition was observed upon cooling to 100 K, where essentially the same structure was obtained with a = 6.989 Å. Upon heating, NaSeC2H releases C2H2 as revealed by thermal analysis (DSC/TGA) resulting in potential Na2Se2C2 crystallizing in a small cubic unit cell with a ≈ 3.899 Å similar to findings on the decomposition of the other AISeC2H compounds.

Local Structure and Magnetism of Fe2O3 Maghemite Nanocrystals: The Role of Crystal Dimension.

Here we report on the impact of reducing the crystalline size on the structural and magnetic properties of γ-Fe2O3 maghemite nanoparticles. A set of polycrystalline specimens with crystallite size ranging from ~2 to ~50 nm was obtained combining microwave plasma synthesis and commercial samples. Crystallite size was derived by electron microscopy and synchrotron powder diffraction, which was used also to investigate the crystallographic structure. The local atomic structure was inquired combining pair distribution function (PDF) and X-ray absorption spectroscopy (XAS). PDF revealed that reducing the crystal dimension induces the depletion of the amount of Fe tetrahedral sites. XAS confirmed significant bond distance expansion and a loose Fe-Fe connectivity between octahedral and tetrahedral sites. Molecular dynamics revealed important surface effects, whose implementation in PDF reproduces the first shells of experimental curves. The structural disorder affects the magnetic properties more and more with decreasing the nanoparticle size. In particular, the saturation magnetization reduces, revealing a spin canting effect. Moreover, a large effective magnetic anisotropy is measured at low temperature together with an exchange bias effect, a behavior that we related to the existence of a highly disordered glassy magnetic phase.

Anomalous High Temperature Structural Behavior of Potential Multifunctional Material SmCo0.5Cr0.5O3

Crystal structure parameters of the mixed cobaltite–chromite SmCo0.5Cr0.5O3 in the temperature range of 298–1173 K were derived from in situ high‐resolution X‐ray synchrotron powder diffraction data. Similar to the parent SmCoO3 compound, SmCo0.5Cr0.5O3 reveals anomalous thermal expansion reflected in abnormal temperature dependence of the unit cell dimensions and the selected interatomic distances and angles. These anomalies are associated with temperature induced changes of spin state of Co3+ ions and coupled insulator‐metal transition. Observed decreasing behavior of the bandwidth W points on the increasing population of the exited spin states of Co3+ ions in SmCo0.5Cr0.5O3 with increasing temperature. First principle calculations revealed antiferromagnetic ground state of SmCo0.5Cr0.5O3 as the most stable.

Na-Ni-H Phase Formation at High Pressures and High Temperatures: Hydrido Complexes [NiH5]3- Versus the Perovskite NaNiH3.

The Na–Ni–H system was investigated by in situ synchrotron diffraction studies of reaction mixtures NaH–Ni–H2 at around 5, 10, and 12 GPa. The existence of ternary hydrogen-rich hydrides with compositions Na3NiH5 and NaNiH3, where Ni attains the oxidation state II, is demonstrated. Upon heating at ∼5 GPa, face-centered cubic (fcc) Na3NiH5 forms above 430 °C. Upon cooling, it undergoes a rapid and reversible phase transition at 330 °C to an orthorhombic (Cmcm) form. Upon pressure release, Na3NiH5 further transforms into its recoverable Pnma form whose structure was elucidated from synchrotron powder diffraction data, aided by first-principles density functional theory (DFT) calculations. Na3NiH5 features previously unknown square pyramidal 18-electron complexes NiH53–. In the high temperature fcc form, metal atoms are arranged as in the Heusler structure, and ab initio molecular dynamics simulations suggest that the complexes are dynamically disordered. The Heusler-type metal partial structure is essentially maintained in the low temperature Cmcm form, in which NiH53– complexes are ordered. It is considerably rearranged in the low pressure Pnma form. Experiments at 10 GPa showed an initial formation of fcc Na3NiH5 followed by the addition of the perovskite hydride NaNiH3, in which Ni(II) attains an octahedral environment by H atoms. NaNiH3 is recoverable at ambient pressures and represents the sole product of 12 GPa experiments. DFT calculations show that the decomposition of Na3NiH5 = NaNiH3 + 2 NaH is enthalpically favored at all pressures, suggesting that Na3NiH5 is metastable and its formation is kinetically favored. Ni–H bonding in metallic NaNiH3 is considered covalent, as in electron precise Na3NiH5, but delocalized in the polyanion [NiH3]−.

Manipulating Spin Alignments of (Y,Lu)1.7Fe17 Intermetallic Compounds via Unusual Thermal Pressure.

External pressure has been successfully employed to achieve desirable spin alignments in the field of materials science but is seriously restricted by the difficulty of reaching high pressure with conventional methods. The search for simple and effective ways to apply pressure on the lattice is challenging but intriguing. Here we report a new strategy to manipulate the spin alignments of (Y,Lu)1.7Fe17 intermetallic compounds through unusual thermal pressure. The spin alignments of Fe initially lie parallel inside the basal plane and then turn spirally between adjacent layers with a zone axis along the c direction under higher Lu concentration. The synchrotron and neutron powder diffraction investigations clearly reveal that the direction of spin alignments is highly correlated to large lattice contraction induced by negative thermal expansion (NTE), an unusual thermal pressure, along the c direction. The critical lattice parameter c to form spiral spin alignments is determined unambiguously. This work presents a feasible way to adjust spin alignments through NTE, which might be conducive to the future design of particular spin alignments instead of physical pressure for functional magnetic materials.

Fast continuous measurement of synchrotron powder diffraction synchronized with controlling gas and vapour pressures at beamline BL02B2 ofSPring-8.

A gas- and vapour-pressure control system synchronized with the continuous data acquisition of millisecond high-resolution powder diffraction measurements was developed to study structural change processes in gas storage and reaction materials such as metal organic framework compounds, zeolite and layered double hydroxide. The apparatus, which can be set up on beamline BL02B2 at SPring-8, mainly comprises a pressure control system of gases and vapour, a gas cell for a capillary sample, and six one-dimensional solid-state (MYTHEN) detectors. The pressure control system can be remotely controlled via developed software connected to a diffraction measurement system and can be operated in the closed gas and vapour line system. By using the temperature-control system on the sample, high-resolution powder diffraction data can be obtained under gas and vapour pressures ranging from 1 Pa to 130 kPa in temperatures ranging from 30 to 1473 K. This system enables one to perform automatic and high-throughput in situ X-ray powder diffraction experiments even at extremely low pressures. Furthermore, this developed system is useful for studying crystal structures during the adsorption/desorption processes, as acquired by millisecond and continuous powder diffraction measurements. The acquisition of diffraction data can be synchronized with the control of the pressure with a high frame rate of up to 100 Hz. In situ and time-resolved powder diffraction measurements are demonstrated for nanoporous Cu coordination polymer in various gas and vapour atmospheres.

Powder X-ray diffraction of fluorometholone, C22H29FO4

Commercial fluorometholone, CAS #426-13-1, crystallizes in the monoclinic space group P21 (#4) with a = 6.40648(2), b = 13.43260(5), c = 11.00060(8) Å, β = 92.8203(5)°, V = 945.517(5) Å3, and Z = 2. A reduced cell search in the Cambridge Structural Database yielded one previous structure determination, using single-crystal data at 292 K. In this work, the sample was ordered from the United States Pharmacopeial Convention (Lot # R032K0) and analyzed as-received. The room temperature (295 K) crystal structure was refined using synchrotron (λ = 0.412826 Å) powder diffraction data and optimized using density functional theory (DFT) techniques. Hydrogen positions were included as a part of the structure and were re-calculated during the refinement. The diffraction data were collected on beamline 11-BM at the Advanced Photon Source, Argonne National Laboratory, and the powder X-ray diffraction pattern of the compound has been submitted to ICDD® for inclusion in the Powder Diffraction File™. The agreement of the Rietveld-refined and DFT-optimized structures is excellent; the root-mean-square Cartesian displacement is 0.060 Å. In addition to the O–H⋯O hydrogen bonds observed by Park et al. (Park, Y. J., Lee, M. Y., and Cho, S. I. (1992). “Fluorometholone,” J. Korean Chem. Soc. 36, 812–817), C–H⋯O hydrogen bonds contribute to the crystal energy.

KxRb2–xPdC2: A Solid Solution of a Quaternary Acetylide with Vegard Behavior

By reacting the ternary acetylides K2PdC2 and Rb2PdC2 at 300 °C under inert conditions a complete solid solution KxRb2–xPdC2 with x = 0–2 was obtained, which was followed and confirmed by synchrotron powder diffraction data. This solid solution shows ideal Vegard behavior, as predicted by Hume‐Rothery rules for ΔV < 15 % (ΔV = 9.2 % for K+/Rb+). According to the powder diffraction data the formation of the quaternary acetylides seems to occur via diffusion of the alkali metal ions, whereas the 1∞[Pd0(C2)2/22–] chains remain unaffected during this reaction.