Diopside Structure Research Articles

Synthesis and structural characterization of CaMg0.5CoxNi0.5-xSi2O6 (0 ≤ x ≤ 0.5) solid solutions as a colouring substance

In this study, CaMg0.5CoxNi0.5-xSi2O6 (0.0 ≤ x ≤ 0.5) solid solutions with a diopside structure were prepared to reduce the cobalt and nickel amounts compared to M2SiO4 or MgMSiO4 (M = Co, Ni) compounds or CaCoxNi1-xSi2O6 solid solutions. Colloidal gels were obtained by adding an ammonia aqueous solution to the suspensions of precursors in aqua until pH = 10. Diopside structure began to develop at 800 °C and at 1000–1200 °C crystallinity and pink colour of materials (x ≠ 0) are optimal. In both CaMg0.5CoxNi0.5-xSi2O6 (0.0 ≤ x ≤ 0.5) and MgCoxNi1-xSiO4 (0.0 ≤ x ≤ 1.0) solid solutions with diopside and olivine structures the position of the third transition of octahedral Co(II), 4T1 → 4T1(P), is centred into the green absorption range and the observed colour is pink. A higher red amount in diopside than in olivine structure can be explained by the minor width of band of this third transition (minor distortion of octahedral M1 site) and shorter mean M1-O distances (M = Ni, Co).

Pure and Sc-doped diopside (CaMgSi2O6) vibrational spectra: modelling and experiments.

We investigated the structure of pure and Sc-doped synthetic diopside (a monoclinic single-chain silicate nominally CaMgSi2O6); in Sc-doped diopside, Sc3+ substitutes Mg2+ in the structure and, to achieve charge balance, vacancies form at the expense of Ca2+. We compared the structure obtained from ab initio modelling techniques at the density functional theory (DFT) level with the structure solved by employing single crystal X-ray diffraction. Furthermore, we compared IR and Raman spectroscopy experiments with vibrational density of states (VDOS) calculated from the Fourier transform of the velocity autocorrelation function obtained using ab initio (DFT) molecular dynamics simulations. In this framework, we developed a computational tool to assign the vibrational mode associated with a specific frequency. This method consists of projecting velocities along a specific set of internal coordinates such as stretching or bending, in cases involving defects or vacancies, to calculate a partial VDOS (pVDOS) that takes into account only the vibrations associated with selected internal modes, aiding the interpretation of the total VDOS and the experimental spectra in a relevant way. The computed data were validated with the experiments and we observed that doping the diopside structure with Sc produces peak broadening and the occurrence of new peaks in the Raman spectra and that site vacancies are associated with the nearby Sc site. The present work constitutes an interesting starting point to exploit the calculated VDOS/pVDOS to characterize experimental vibrational spectra of complex systems containing local vacancies, substitutions or defects as the Sc-doped diopside.

Site preference-based luminescence studies in Eu doped calcium magnesium silicate phosphor: A combined experimental and DFT approach

The luminescence of Eu3+ doped calcium magnesium silicate (CMS: Eu3+) phosphor is studied experimentally by optimizing the single diopside structure in the solid state reaction method and theoretically verified using the first principle density functional theory (DFT) calculation. Field Emission Scanning Electron Microscopy (FESEM) analysis shows a transition from agglomerated morphology to particle formation at 900 °C. A combination of diopside and akermanite structures are formed at 800 °C, whereas a single diopside phase is optimized from 900 °C onwards. DFT calculation has been carried out to identify the lattice parameters of the diopside structure of calcium magnesium silicate (CMS) and Eu3+ doped CMS by replacing Eu3+ in the lattice site of Ca and Mg to identify the stable structure. The lattice expansion is minimal when Eu3+ replaces the Ca2+ position. Lattice parameters of the diopside phase calculated using Rietveld refinement of the XRD pattern are in agreement with DFT findings. FTIR analysis confirms a redshift corresponding to Ca–O and a blueshift corresponding to Mg–O stretching wavenumbers due to the structural modification of CMS due to Eu addition in the lattice. The stability and site preference of Eu3+ ion in CMS is determined from the mixing energy (ΔHm) of Eu doped in the Ca site and Mg site of CMS separately via DFT calculation and confirm that the mixing energy is minimum when Eu3+ replaces Ca lattice position. UV–visible, DRS spectroscopy confirms a bandgap of ∼6 eV for CMS and CMS: Eu3+. Luminescence studies confirm constant peak splitting in the 5D0→7FJ (J = 1,2,4) transitions due to the crystal field effect caused due to the incorporation of Eu3+ in the diopside structure with dodecahedral coordination. Eight coordinated site preference of Eu3+ in diopside is confirmed via DFT calculations. Modification in asymmetry ratio (R-ratio) with temperature also corroborates with modification in the intensity of photoluminescence spectra dictated by the reduction in inversion symmetry. CIE color chromaticity analysis shows a coordinate of (0.61, 0.39) in the red region of visible spectra with a color purity of 83.49% irrespective of annealing temperature.

Structure of diopside, enstatite, and magnesium aluminosilicate glasses: A joint approach using neutron and x-ray diffraction and solid-state NMR.

Neutron diffraction with magnesium isotope substitution, high energy x-ray diffraction, and 29Si, 27Al, and 25Mg solid-state nuclear magnetic resonance (NMR) spectroscopy were used to measure the structure of glassy diopside (CaMgSi2O6), enstatite (MgSiO3), and four (MgO)x(Al2O3)y(SiO2)1-x-y glasses, with x = 0.375 or 0.25 along the 50 mol. % silica tie-line (1 - x - y = 0.5) or with x = 0.3 or 0.2 along the 60 mol. % silica tie-line (1 - x - y = 0.6). The bound coherent neutron scattering length of the isotope 25Mg was remeasured, and the value of 3.720(12) fm was obtained from a Rietveld refinement of the powder diffraction patterns measured for crystalline 25MgO. The diffraction results for the glasses show a broad asymmetric distribution of Mg-O nearest-neighbors with a coordination number of 4.40(4) and 4.46(4) for the diopside and enstatite glasses, respectively. As magnesia is replaced by alumina along a tie-line with 50 or 60 mol. % silica, the Mg-O coordination number increases with the weighted bond distance as less Mg2+ ions adopt a network-modifying role and more of these ions adopt a predominantly charge-compensating role. 25Mg magic angle spinning (MAS) NMR results could not resolve the different coordination environments of Mg2+ under the employed field strength (14.1T) and spinning rate (20kHz). The results emphasize the power of neutron diffraction with isotope substitution to provide unambiguous site-specific information on the coordination environment of magnesium in disordered materials.

Synthesis, phase composition and characterization of Co-diopside ceramic pigments

Ceramic pigments in the system CaO – CoO – MgO – 2SiO2 were synthesized through solid-state high temperature sintering at 1000, 1100 and 1200 °C. The starting compositions were determined from the stoichiometric mineral diopside, following the expression CaO.xCoO.(1-x)MgO·2SiO2, where x = 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.5, 0.7 and 0.9. The effect of sintering temperature and initial cobalt concentration on the phase composition and colour were studied by powder X-ray diffraction analysis, scanning electron microscopy (SEM), infrared (FT-IR), ultraviolet–visible - (UV–Vis) and electron paramagnetic resonance (EPR) spectroscopy. Poly-phase ceramics were obtained depending on synthesis parameters, which in addition to Co-diopside, may contain wollastonite, Co-åckermanite – Ca2(Co, Mg)Si2O7, Co-olivine – CoMgSiO4, Co-monticellite – Ca(Mg, Co) SiO4, and cristobalite. Quantitative ratios of detected mineral phases and the degree of cobalt isomorphic substitution were determined by applying Rietveld refinement approach. Trends and consistencies were outlined revealing that concentration of cobalt in the initial synthesis batch and its isomorphous incorporation in the crystal structure of diopside affect the structural perfection of the cation polyhedra. This fact obviously plays a key role in controlling the amount of the main constituent phase in the run-product. Ceramics of highest diopside content and lowest measured degree of structural distortion were only formed at 1200 °C and initial cobalt concentration in the range x = 0.2–0.3. These samples are pink in colour and have the highest value of red coordinate in the CIELab system due to Co2+ ions in octahedral coordination in diopside structure.

Luminescence studies of Eu3+ doped calcium magnesium silicate phosphor prepared at different annealing temperatures for fine color tunability

This research article explores the possibility of fine-tuning of the color monochromaticity of Eu3+ doped calcium magnesium silicate: CaMgSi2O6: Eu3+, Ca3MgSi2O8: Eu3+, and Ca2MgSi2O7: Eu3+ (CMS: Eu3+) phosphor by introducing a crystal field effect in the luminescence emission spectra. The effect of Eu doping and annealing temperature on modifying the morphology, crystal structure, bonding nature, luminescent properties, and color monochromaticity of calcium magnesium silicate; CaMgSi2O6, Ca3MgSi2O8, and Ca2MgSi2O7 (CMS) phosphor is analyzed in detail. CMS and CMS: Eu3+ were separately prepared by the sol-gel method, employing five different annealing temperatures. Morphological analysis using FESEM confirmed agglomerated porous structures at annealing temperatures of 800 °C, 900 °C, and 1000 °C, whereas clear particle formation was observed at 1100 °C and 1200 °C, both in CMS and CMS: Eu3+. An increase in the particle size with temperature and reduction in the growth kinetics with Eu3+ doping was noticed. The non-stoichiometric composition identified during the chemical analysis was in agreement with the XRD findings of the formation of merwinite, diopside, and akermanite phases in CMS and CMS: Eu3+. The XRD analysis further confirmed that Eu3+ doping favor merwinite over diopside structure. The structural modifications in the CMS due to the presence of Eu3+ appeared as blue and redshift in the vibrational wavenumbers of Ca–O and Mg–O in FTIR studies. Luminescence studies confirmed an increase in the peak splitting with the annealing temperature in the excitation and the emission spectra due to the crystal field effect. The possible reasons for the peak splitting are the formation of multiple phases with multiple site occupancy, preferably with the octahedral coordination, and the J mixing due to the effective charge balancing expected due to higher oxygen capture occurring at the higher annealing temperature. With the increase in annealing temperature, color chromaticity coordinates varied from (0.61, 0.39) to (0.63, 0.37) due to better charge compensation which is in agreement with the luminescence studies.

High performing additively manufactured bone scaffolds based on copper substituted diopside

The inclusion of small amounts of copper is often reported to enhance the mechanical and biointegrative performance of bioceramics towards tissue engineering applications. In this work, 3D scaffolds were additively manufactured by robocasting of precipitation derived copper doped diopside. Compositions were chosen in which magnesium sites in diopside were substituted by copper up to 3 at.%. Microstructure, mechanical performance, bioactivity, biodegradability, drug release, biocompatibility, in vitro angiogenesis and antibacterial activity were studied. Results indicate that copper is incorporated in the diopside structure and improves materials’ fracture toughness. Scaffolds with > 80% porosity exhibited compressive strengths exceeding that of cancellous bone. All compositions showed bioactivity and drug release functionalities. However, only samples with 0–1 at.% copper substitution showed favorable proliferation of osteogenic sarcoma cells, human umbilical vein endothelial cells and fibroblasts, while larger amounts of copper had cytotoxic behavior. In vitro angiogenesis was significantly enhanced by low levels of copper. Copper-containing materials showed anti-Escherichia coli activity, increasing with copper content. We show that across multiple indicators, copper substituted diopside of the composition CaMg0.99Cu0.01Si2O6, exhibits high performance as a synthetic bone substitute, comparing favorably with known bioceramics. These findings present a pathway for the enhancement of bioactivity and mechanical performance in printable bioceramics.

Pyroxenite-Based Ceramic Pigment

A composition of a ceramic pigment has been developed using pyroxenite, including pyroxene minerals — augite and enstatite—with forsterite, serpentine and coloring oxides of iron and chromium being present. The compositions of the crystalline phases in pigments were investigated by means of XPAand microanalysis as a function of the firing temperature. A ceramic pigment with diopside structure makes it possible to obtain a brown coating when using the pigment in a wide range of firing temperatures 850 – 1250°C, excluding melting of the pigment while improving the purity of tone and brightness of the coating.

Incorporation of monovalent cations into diopside to improve biomineralization and cytocompatibility

This paper aims to evaluate the structure, bioactivity, biodegradation and cytocompatibility of diopside (CaMgSi2O6) doped with 2 mol% of Li, Na and K separately substituting for 1 mol% of Mg of diopside. An ethanolic, inorganic-salt coprecipitation method, followed by calcination at 900 °C, was used for synthesis. X-ray diffraction showed that the single-phase diopside structure is kept at this level of substitution; however, the crystallinity and lattice volume of diopside were changed depending on the size difference of the replacement components. According to in vitro biological studies, doping of all the alkali ions improves the bioactivity of diopside, with the highest and least effects obtained by K and Na, respectively. The MTT assay of osteoblast-like MG-63 cell cultures indicated that the cell viability and proliferation are improved as a result of using all the dopants, where the most enhancements were found for Na and K. It is eventually concluded that the incorporation of K into diopside ensures the optimal behaviors in terms of bioactivity and biocompatibility in vitro.

Structure, biomineralization and biodegradation of Ca-Mg oxyfluorosilicates synthesized by inorganic salt coprecipitation

Abstract In this research, a novel group of Ca-Mg oxyfluorosilicates containing different levels of fluoride substituting for oxide was synthesized by an inorganic salt coprecipitation process followed by calcination/sintering. The effects of the incorporation of fluoride on the resultant structural characteristics, apatite-forming ability and biodegradability were evaluated by X-ray diffraction, transmission electron microscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, inductively coupled plasma spectroscopy and pH measurements. According to the results, the samples containing up to 2 mol% F present a single-phase structure of diopside (MgCaSi 2 O 6 ) doped with F. It was also found that to meet the most biomineralization characteristic, the optimal value of fluoride in the homogeneous samples is 1 mol%. In this regard, on the one hand, the partial incorporation of fluoride into apatite (via forming fluorohydroxyapatite) and, on the other hand, the absence of fluorite (CaF 2 ) as a consumer of Ca in the deposits are responsible for achieving the most apatite-forming ability circumstance controlled by an ion-exchange reaction mechanism. In conclusion, this study reflects the merit of the optimization of fluoride-doping into Ca-Mg silicates for development in biomedicine.

Crystal chemistry of Sc-bearing synthetic diopsides

Scandium substitution in the diopside structure was studied by single-crystal X-ray diffraction on a series of synthetic diopside samples. These diopsides were doped with increasing amounts of Sc3+ through a coupled substitution involving M1(Sc3+)1 M2[] 1 T (B)1 M1(Mg2+)−1 M2(Ca2+)−1 T(Si4+)−1 exchange, whereby charge compensation is achieved by vacancies at the M2 sites and B at the tetrahedral sites. The substitution of scandium for magnesium at the M1 site results in an increase in volume and distortion of the M1O6 polyhedron. The accompanying creation of vacancies at the M2 sites causes an increase in the M2 polyhedral volume. The modifications of the M1 and M2 polyhedra result in an increase of the polyhedral strip along the b lattice direction and a straightening of the tetrahedral chain. The geometrical modification of the M1 polyhedron due to scandium incorporation is comparable to those observed when similar amounts of Ti3+/Ti4+ substitute for Mg in the diopside structure, suggesting a structural control on the solubility of Sc and Ti in diopside that may influence the extent of the solid solutions between the Sc and Ti end-members.

Determination of the crystal structure of diopside (Ca0.8Fe0.2)(Mg0.8Fe0.2)Si2O6 from the Gazakh Trough (Azerbaijan)

The crystal structure of a clinopyroxene is determined by X-ray diffraction. The unit cell parameters are as follows: a = 9.732(7) A, b = 8.896(6) A, c = 5.280(4) A, and β = 106.160(11)°; V = 439.1(5) A3; space group C2/c; and Z = 4. The structure is determined by the direct method and refined in the anisotropic approximation by the full-matrix least-squares method (R[F 2 > 2σ(F 2)] = 0.027, wR(F 2) = 0.072). According to the results of the X-ray structure analysis, the crystal chemical formula of the compound is (Ca0.8Fe0.2)(Mg0.8Fe0.2)Si2O6. In the structure, columns of (Mg, Fe)-octahedra are connected on two sides with Si2O6 chains. The resulting structural units have the [(Mg,Fe)2(Si2O6)2]4− composition. These units form a heterogeneous framework, which is typical of all pyroxene structures. The [(Mg,Fe)2(Si2O6)2]2− composition of the framework corresponds to the ratio [(Mg,Fe) + Si]: O = 3: 6 (1: 2). The (Ca, Fe) atoms are located in the holes of the framework.

Effect of some rare-earth oxides on structure, devitrification and properties of diopside based glasses

Four diopside based glasses containing an equimolar concentration of different rare-earth oxides (La 2O 3, Nd 2O 3, Gd 2O 3 and Yb 2O 3) respectively, were obtained by melt-quenching technique. Structural and thermal behaviour of the glasses was investigated by density and molar volume, infrared spectroscopy (FTIR), dilatometry, and scanning electron microscopy (SEM). All the glasses exhibited amorphous phase separation. The crystallization behaviour of the glasses was investigated by using differential thermal analysis (DTA). Sintering, crystallization, microstructure, and properties of the glass-ceramics were investigated under non-isothermal heating conditions in the temperature range of 800–900 °C.

Effect of mineralizers on the synthesis of ceramic pigments from talc

The mineralizing effect of sodium fluoride, boric acid, and a natural fluorine-bearing mineral (topaz concentrate) on the synthesis from talc of ceramic pigments with magnesium metasilicate, forsterite, and diopside structures is investigated. It is shown that NaF is the most active mineralizer. It is noted that NaF has a positive effect not only on the synthesis of crystalline structure but also on the chromaticity of the pigments. The pigment compositions developed can be widely used to tint ceramic pastes, glazes and glasses, in the manufacture of building materials, and to make paints.

The compressibility and high pressure structure of diopside from first principles simulation

The structure of diopside (CaMgSi2O6) has been calculated at pressures between 0 and 25 GPa using the planewaves and pseudopotentials approach to density functional theory. After applying a pressure correction of 4.66 GPa to allow for the under-binding usually associated with the generalized gradient approximation, cell parameters are in good agreement with experiment. Fitting to the third-order Birch–Murnaghan equation of state yields values of 122 GPa and 4.7 for the bulk modulus and its pressure derivative. In addition to cell parameters, our calculations provide all atomic positional parameters to pressures considerably beyond those currently available from experiment. We have analyzed these data in terms of polyhedral rigidity and regularity and find that the most compressible Ca polyhedron becomes markedly less anisotropic above 10 GPa.

The crystal structure of diopside at pressure to 10 GPa

The crystal structure of diopside has been determined at various pressures to 10.16 GPa. The results to 5 GPa are consistent with Levien and Prewitt (1981). The crystal structures have been analyzed using the geometric pyroxene model of Thompson and Downs (2004), the anion packing algorithm of Thompson and Downs (2001), and a new algorithm that quantifies the distortion of observed pyroxenes from their geometric model equivalents. Diopside is shown to compress via three main mechanisms: isotropic scaling, kinking of the tetrahedral chains, and collapse of the M1 chain toward its axis. The kinking of the chains accounts for most of the anisotropy of compression observed in the a-c plane, and the collapse of the M1 chain explains the anisotropy seen in the b-c plane. Model behavior is shown to reproduce many of the observations of previous workers. Anion-anion interactions are shown to be important in the distortion of observed diopside from its geometric model equivalent.

Production of ceramic pigments with wollastonite and diopside structures using nepheline sludge

Ceramic pigments with wollastonite and diopside structures were obtained by using nepheline sludge in charge adjustment with magnesium and silicon oxides. The pigments are resistant to high temperatures and the effect of fluxes and glazes. They can be recommended to complement pigments of spectral colors and for bulk coloring of ceramic pastes and glazes. In addition to lowering the price of the pigments, problems of using nonutilizable production wastes are solved and the raw-material base for synthesis of ceramic pigments is expanded.

Crystallization behaviour, structure and properties of sintered glasses in the diopside–Ca-Tschermak system

Four glasses with nominal compositions of CaMg 0.8Al 0.4Si 1.8O 6, CaMg 0.75Al 0.5Si 1.75O 6, CaMg 0.7Al 0.6Si 1.7O 6, and CaMg 0.65Al 0.7Si 1.65O 6, were successfully obtained by melting in alumina crucibles at 1580 °C for 1 h, aiming at producing glass ceramics based on diopside–Ca-Tschermak. Sintering and crystallization behaviour of the glasses, coupled with calculation of the activation energy of crystallization, were investigated upon heat treatment under different conditions of heating rates (5–40 K/min), temperatures (850–1000 °C), and times (1–300 h). The experimental results showed that there is a threshold of Ca-Tschermak solubility in diopside structure at ca. 30 mol.%, which is technologically important with regard to the production of mono-mineral glass ceramics. The good matching of thermal properties and the strong adherence to yttria stabilized cubic zirconia indicate the investigated glass ceramics for further experimentation as candidates for SOFC sealants.

Production of ceramic pigments with diopside and anorthite structure using the gel method

The possibility of producing ceramic pigments with the diopside and anorthite structures by the sol-gel method using wollastonite is studied. It is established that the use of the gel method intensifies the synthesis of anorthite and diopside crystal structures by means of better homogenization of the batch components at the mixing stage. A positive factor is the effective formation of anorthite and diopside structures at relatively low temperatures (about 1100°C), as well as the mineralizing effect of the chromophores on the crystallization of these minerals.

Crystallization and properties of glasses based on diopside–Ca-Tschermak’s–fluorapatite system

The crystallization characteristics of glasses based on compositions in the diopside [CaMgSi 2O 6]–Ca-Tschermak’s [CaAl 2SiO 6]–fluorapatite [Ca 5(PO 4) 3F] system have been investigated. The effect of Ca-Tschermak’s/diopside replacement, at constant Ca 5(PO 4) 3F content, on the crystallization characteristics of the glasses and the solid solution phases formed, as well as the resulting microstructure, are traced by differential thermal analysis (DTA), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Various pyroxene solid solutions together with fluorapatite phases are detected by XRD analysis. There is a preferential tendency for diopside to capture Ca-Tschermak’s in its structure forming pyroxene solid solution of diopsidic type. The maximum concentration of CaAl 2SiO 6 that could be accommodated in the diopside structure was 25%. Above this percentage, gehlenite Ca 2Al 2SiO 7 also developed. However, there was no solid solution formed between pyroxene and fluorapatite. The thermal expansion coefficients ( α-values) and microhardness of the glasses and glass–ceramics were determined. The data of the glasses were correlated to the internal structure of the glasses, nature and role played by glass forming cations. However, the properties of the crystalline glasses were mainly attributed to different factors including the crystalline phases formed, residual glassy phase and the microstructures.