High-resolution X-ray Powder Diffraction Research Articles

Acemetacin cocrystal structures by powder X-ray diffraction.

Cocrystals of acemetacin drug (ACM) with nicotinamide (NAM), p-aminobenzoic acid (PABA), valerolactam (VLM) and 2-pyridone (2HP) were prepared by melt crystallization and their X-ray crystal structures determined by high-resolution powder X-ray diffraction. The powerful technique of structure determination from powder data (SDPD) provided details of molecular packing and hydrogen bonding in pharmaceutical cocrystals of acemetacin. ACM-NAM occurs in anhydrate and hydrate forms, whereas the other structures crystallized in a single crystalline form. The carboxylic acid group of ACM forms theacid-amide dimer three-point synthon R32(9)R22(8)R32(9) with three different syn amides (VLM, 2HP and caprolactam). The conformations of the ACM molecule observed in the crystal structures differ mainly in the mutual orientation of chlorobenzene fragment and the neighboring methyl group, being anti (type I) or syn (type II). ACM hydrate, ACM-NAM, ACM-NAM-hydrate and the piperazine salt of ACM exhibit the type I conformation, whereas ACM polymorphs and other cocrystals adopt the ACM type II conformation. Hydrogen-bond interactions in all the crystal structures were quantified by calculating their molecular electrostatic potential (MEP) surfaces. Hirshfeld surface analysis of the cocrystal surfaces shows that about 50% of the contribution is due to a combination of strong and weak O⋯H, N⋯H, Cl⋯H and C⋯H interactions. The physicochemical properties of these cocrystals are under study.

Experimental Evidence for Static Charge Density Waves in Iron Oxypnictides.

In this Letter we report high-resolution synchrotron x-ray powder diffraction and transmission electron microscope analysis of Mn-substituted LaFeAsO samples, demonstrating that a static incommensurate modulated structure develops across the low-temperature orthorhombic phase, whose modulation wave vector depends on the Mn content. The incommensurate structural distortion is likely originating from a charge-density-wave instability, a periodic modulation of the density of conduction electrons associated with a modulation of the atomic positions. Our results add a new component in the physics of Fe-based superconductors, indicating that the density wave ordering is charge driven.

One step pyro-synthesis process of nanostructured Li3V2(PO4)3/C cathode for rechargeable Li-ion batteries

A monoclinic Li3V2(PO4)/C (LVP/C) with nanostructured morphology was synthesized via a one-step pyro-synthesis, for use as cathode material in rechargeable Li-ion batteries. Highly crystalline LVP/C nanoparticles can be obtained without additional heat treatment. The structural properties and morphology of the sample were studied using various analyses, including high resolution powder X-ray diffraction (HRPD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The LVP/C cathode exhibited initial discharge capacities of 139 and 190.3mAhg−1 within the potential windows of 3–4.3V and 3–4.8V, respectively. These results indicate that the formation of nanosized particles and the presence of amorphous carbon layer influence the electrochemical properties LVP/C electrode. Specifically, the present pyro-synthesis strategy facilitates the production of LVP cathode materials with improved cyclability and rate capability under a very short reaction time.

Systematic study of the crystallization process of CrAPO-5 using in situ high resolution X-ray diffraction

Systematic study of the hydrothermal crystallization process of CrAPO-5 by in situ high resolution X-ray powder diffraction (HRXRD).

Mixed-linker UiO-66: structure-property relationships revealed by a combination of high-resolution powder X-ray diffraction and density functional theory calculations.

The use of mixed-linker metal-organic frameworks (MIXMOFs) is one of the most effective strategies to modulate the physical-chemical properties of MOFs without affecting the overall crystal structure. In many instances, MIXMOFs have been recognized as solid solutions, with random distribution of ligands, in agreement with the empirical rule known as Vegard's law. In this work, we have undertaken a study combining high-resolution powder X-ray diffraction (HR-PXRD) and density functional theory (DFT) calculations with the aim of understanding the reasons why UiO-66-based amino- and bromo-functionalized MIXMOFs (MIXUiO-66) undergo cell expansion obeying Vegard's law and how this behaviour is related to their physical-chemical properties. DFT calculations predict that the unit cell in amino-functionalized UiO-66 experiences only minor expansion as a result of steric effects, whereas major modification to the electronic features of the framework leads to weaker metal-linker interaction and consequently to the loss of stability at higher degrees of functionalization. For bromo-functionalized UiO-66, steric repulsion due to the size of bromine yields a large cell expansion, but the electronic features remain very similar to pristine UiO-66, preserving the stability of the framework upon functionalization. MIXUiO-66 obtained by either direct synthesis or by post-synthetic exchange shows Vegard-like behaviour, suggesting that both preparation methods yield solid solutions, but the thermal stability and the textural properties of the post-synthetic exchanged materials do not display a clear dependence on the chemical composition, as observed for the MOFs obtained by direct synthesis.

Synchrotron X-ray diffraction studies of $\beta $-Ca$_{2-x}M_{x}$SiO$_{4}$ ($M$ = Mg and Sr)

The structures of Mg- and Sr-doped $\beta $-Ca$_{2}$SiO$_{4}$ have been established from high-resolution synchrotron X-ray powder diffraction. These silicates are all isostructural and the structures have been refined in the monoclinic space group, $P$2$_{1}$/$n$. As expected based on size arguments, the cell parameters increase as the amount of Sr increases and likewise decrease as the amount of Mg increases due the size effects of the dopant cation. In all cases the SiO$_{4}$ tetrahedra are essentially regular.

In situ high-resolution powder X-ray diffraction study of UiO-66 under synthesis conditions in a continuous-flow microwave reactor

Large scale synthesis of metal–organic frameworks (MOFs) is of high interest, due to their potential for industrial applications. The capacity to synthesize large amounts of MOFs should be combined with the ability to control their properties. Understanding how process parameters influence the formation of the product is necessary to synthesize tailor-made materials. The crystallization process of a MOF from the reaction mixture can be conveniently monitored in real time by performing in situ studies using synchrotron radiation. This yields insight into the formation of the product under the actual reaction conditions. In this work, we performed an in situ high-resolution powder X-ray diffraction study of the crystallization of UiO-66 in a recently developed continuous-flow microwave reactor that provided excellent performances in terms of space-time yield and atom economy. The effect of the addition of different amounts of water and acetic acid to the reaction mixture on the yield and crystallite size of the product was investigated over a range of residence times. UiO-66 was the only crystalline phase observed and two stages of the process were identified, namely, a preliminary stage, where the crystallite size of the MOF increases, and a steady state one where the quality of the product is constant. The yield and crystallite size of the product primarily depended on the water/acetic acid ratio, which was the most important parameter determining the rate of product formation. Increasing the absolute amounts of additives at fixed ratios led to a higher yield of larger crystallites, whereas aging of the metal stock solution led to a higher yield of smaller crystallites. Selected experiments were performed offline isolating the solid at the steady state and characterizing it after workup. In this way, we demonstrated that large scale synthesis of UiO-66 with controlled properties can be performed with a continuous-flow microwave reactor.

Accurate stone analysis: the impact on disease diagnosis and treatment.

This manuscript reviews the requirements for acceptable compositional analysis of kidney stones using various biophysical methods. High-resolution X-ray powder diffraction crystallography and Fourier transform infrared spectroscopy (FTIR) are the only acceptable methods in our labs for kidney stone analysis. The use of well-constructed spectral reference libraries is the basis for accurate and complete stone analysis. The literature included in this manuscript identify errors in most commercial laboratories and in some academic centers. We provide personal comments on why such errors are occurring at such high rates, and although the work load is rather large, it is very worthwhile in providing accurate stone compositions. We also provide the results of our almost 90,000 stone analyses and a breakdown of the number of components we have observed in the various stones. We also offer advice on determining the method used by the various FTIR equipment manufacturers who also provide a stone analysis library so that the FTIR users can feel comfortable in the accuracy of their reported results. Such an analysis on the accuracy of the individual reference libraries could positively influence the reduction in their respective error rates.

Spontaneous structural distortion of the metallic Shastry-Sutherland system DyB4 by quadrupole-spin-lattice coupling

DyB4 has a two-dimensional Shastry-Sutherland (Sh-S) lattice with strong Ising character of the Dy ions. Despite the intrinsic frustrations, surprisingly, it undergoes two successive transitions: a magnetic ordering at TN = 20K, and a quadrupole ordering at TQ=12.5 K. From high-resolution neutron and synchrotron X-ray powder diffraction studies, we have obtained full structural information on this material in all phases, and demonstrate that structural modifications occurring at quadrupolar transition lead to the lifting of frustrations inherent in the Sh-S model. Our study thus provides a complete experimental picture of how the intrinsic frustration of the Sh-S lattice can be lifted by the coupling to quadrupole moments. We show that two other factors, i.e. strong spin-orbit coupling and long-range RKKY interaction in metallic DyB4, play an important role in this behavior.

Reentrant Structural and Optical Properties and Large Positive Thermal Expansion in Perovskite Formamidinium Lead Iodide.

The structure of the hybrid perovskite HC(NH2 )2 PbI3 (formamidinium lead iodide) reflects competing interactions associated with molecular motion, hydrogen bonding tendencies, thermally activated soft octahedral rotations, and the propensity for the Pb2+ lone pair to express its stereochemistry. High-resolution synchrotron X-ray powder diffraction reveals a continuous transition from the cubic α-phase (Pm3‾ m, #221) to a tetragonal β-phase (P4/mbm, #127) at around 285 K, followed by a first-order transition to a tetragonal γ-phase (retaining P4/mbm, #127) at 140 K. An unusual reentrant pseudosymmetry in the β-to-γ phase transition is seen that is also reflected in the photoluminescence. Around room temperature, the coefficient of volumetric thermal expansion is among the largest for any extended crystalline solid.

Two cubic phases in kimzeyite garnet from the type locality Magnet Cove, Arkansas.

The crystal structure of an optically anisotropic kimzeyite garnet from Magnet Cove, Arkansas, USA, where it was first discovered, was refined with the Rietveld method, cubic space group, Ia\overline 3 d, and monochromatic [λ = 0.41422 (2) Å] synchrotron high-resolution powder X-ray diffraction (HRPXRD) data. The Rietveld refinement reduced χ2 and overall R(F2) values are 1.840 and 0.0647, respectively. The sample, with the general garnet formula [8]X3[6]Y2[4]Z3[4]O12, contains an intergrowth of two cubic phases that occur initially as oscillatory growth zoning, and patchy intergrowths arise later from fluid-enhanced dissolution and re-precipitation. The two compositions obtained with electron-probe microanalyses (EPMA) are Ca3.00(Zr1.31Ti4+0.46Fe3+0.22Mn3+0.01)∑2[Al0.76Fe3+1.01Si1.23]∑3O12 for phase 1a and Ca2.99(Zr1.48Ti4+0.37Fe3+0.15)∑2[Al0.87Fe3+0.98Si1.15]∑3O12 for phase 1b. The weight percentage, unit-cell parameter (Å), distances (Å), and site occupancy factors (s.o.f.s) for phase 1a are as follows: 42.6 (2)%, a = 12.46553 (3) Å, average 〈X-O〉 = 2.482, Y-O = 2.059 (2), Z-O = 1.761 (2) Å, Ca (X s.o.f.) = 0.960 (4), Zr (Y s.o.f.) = 0.809 (3), and Fe (Z s.o.f.) = 0.623 (2). The corresponding values for phase 1b are 57.4 (2)%, a = 12.47691 (2) Å, average 〈X-O〉 = 2.482, Y-O = 2.062 (1), Z-O = 1.762 (1) Å, Ca (X s.o.f.) = 0.957 (3), Zr (Y s.o.f.) = 0.828 (2) and Fe (Z s.o.f.) = 0.617 (2). The main structural differences between the two phases are in the unit-cell parameter, Δa = 0.01138 Å, Y(s.o.f.), and Y-O distance. Structural mismatch between the two cubic phases in a crystal gives rise to strain-induced optical anisotropy.

Spin and orbital disordering by hole doping inPr1−xCaxVO3

High-resolution powder x-ray diffraction and single-crystal neutron diffraction were used to investigate the crystal structure and magnetic ordering of the compound $\mathrm{P}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{a}}_{x}\mathrm{V}{\mathrm{O}}_{3}$ ($0\ensuremath{\le}x\ensuremath{\le}0.3$), which undergoes an insulator-to-metal transition for $x\ensuremath{\sim}0.23$. Since the ionic radii of $\mathrm{P}{\mathrm{r}}^{3+}$ and $\mathrm{C}{\mathrm{a}}^{2+}$ are almost identical and structural disorder is minimal, $\mathrm{P}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{a}}_{x}\mathrm{V}{\mathrm{O}}_{3}$ is a good model system for the influence of hole doping on the spin and orbital correlations in transition metal oxides. The end member $\mathrm{PrV}{\mathrm{O}}_{3}$ is a Mott-Hubbard insulator, which exhibits a structural phase transition at ${T}_{\mathrm{S}}=180\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ from an orthorhombic to a monoclinic structure with space groups Pbnm and $P{2}_{1}/b$, respectively. This transition is associated with the onset of orbital ordering and strong Jahn-Teller distortions of the $\mathrm{V}{\mathrm{O}}_{6}$ octahedra. Antiferromagnetic $C$-type order with vanadium moments oriented in the $ab$ plane is observed below ${T}_{\mathrm{N}}=140\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Upon cooling, the vanadium moments induce a progressive magnetic polarization of the praseodymium sublattice, resulting in a ferrimagnetic structure with coexisting modes (${C}_{x}, {F}_{y}$) and (${F}_{x}, {C}_{y}$). In the insulating range of the $\mathrm{P}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{a}}_{x}\mathrm{V}{\mathrm{O}}_{3}$ phase diagram, Ca doping reduces both the orbital and magnetic transition temperatures so that ${T}_{\mathrm{S}}=108\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{N}}=95\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $x=0.20$. The Jahn-Teller distortions and ordered vanadium moments also decrease upon doping. In a metallic sample with $x=0.30$, Jahn-Teller distortions and long-range orbital ordering are no longer observable, and the average crystal structure remains orthorhombic down to low temperature. However, broadening of some lattice Bragg reflections indicate a significant increase in lattice strain. Antiferromagnetic short-range order with a weak ordered moment of 0.14(3) ${\ensuremath{\mu}}_{\mathrm{B}}$ per vanadium atom could still be observed on the vanadium site below $T\ensuremath{\sim}60\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. We discuss these observations in terms of doping-induced spin-orbital polaron formation.

Accurate unrestrained DDM refinement of crystal structures from highly distorted and low-resolution powder diffraction data.

The structure of benzene:ethane co-crystal at 90 K is refined with anisotropic displacement parameters without geometric restraints from high-resolution synchrotron X-ray powder diffraction (XRPD) data using the derivative difference method (DDM) with properly chosen weighting schemes. The average C-C bond precision achieved is 0.005 Å and the H-atom positions in ethane are refined independently. A new DDM weighting scheme is introduced that compensates for big distortions of experimental data. The results are compared with density functional theory (DFT) calculations reported by Maynard-Casely et al. [(2016). IUCrJ, 3, 192-199] where a rigid-body Rietveld refinement was also applied to the same dataset due to severe distortions of the powder pattern attributable to experimental peculiarities. For the crystal structure of 2-aminopyridinium fumarate-fumaric acid formerly refined applying 77 geometric restraints by Dong et al. [(2013). Acta Cryst. C69, 896-900], an unrestrained DDM refinement using the same XRPD pattern surprisingly gave two times narrower dispersion of interatomic distances.

Relaxor ferroeletric behavior inSr1−xPrxTiO3: Cooperation between polar and antiferrodistortive instabilities

Chemical doping at the Sr and Ti sites is a feasible way to alter the quantum paraelectric state of $\mathrm{SrTi}{\mathrm{O}}_{3}$ perovskite. Doping with Pr is known to induce relaxor ferroelectricity at room temperature in the $\mathrm{S}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{P}{\mathrm{r}}_{x}\mathrm{Ti}{\mathrm{O}}_{3}$ solid solution. The relationship between its dielectric properties and structural phase transition has been debated, but no definitive structural argument has been proposed. Here we present a systematic structural study of $\mathrm{S}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{P}{\mathrm{r}}_{x}\mathrm{Ti}{\mathrm{O}}_{3}$ $(0.020\ensuremath{\le}x\ensuremath{\le}0.150)$. We establish the structural phase diagram using high-resolution x-ray powder diffraction by finding the antiferrodistortive structural phase transitions for all the compositions studied. By using pair distribution function analysis, we show the mismatch between local and long-range structures in terms of increased local order parameters. Finally, we propose a correlation between the local structural order parameters and the emergence of hard polar modes as found by Raman spectroscopy. Our results are quantitatively consistent with recent theoretical calculations showing that the increase of local tetragonality and local octahedral tilting above a critical value in fact underlie the polar instability. This confirms that structural orders involving both polar and antiferrodistortive characters compete and cooperate at different levels, promoting ferroelectricity in $\mathrm{S}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{P}{\mathrm{r}}_{x}\mathrm{Ti}{\mathrm{O}}_{3}$.

Reaction of Pb(II) and Zn(II) with Ethyl Linoleate To Form Structured Hybrid Inorganic-Organic Complexes: A Model for Degradation in Historic Paint Films.

To investigate soap formation in drying oils in historic paints, the reaction between metal acetates (K+, Zn2+, Pb2+) and ethyl linoleate (EL) was studied using optical microscopy, X-ray powder diffraction, and electron microscopy. Pb(II) and Zn(II) react rapidly with EL to form highly structured, spherulitic, luminescent crystallites that aggregate. Evidence from Fourier transform infrared (FTIR) and scanning electron microscopy/energy dispersive X-ray analysis and high-resolution synchrotron powder X-ray diffraction indicates that these are organic–inorganic hybrid complexes or coordination polymers. FTIR absorbance peaks at ca. 1540 cm–1 for Pb(II) and ca. 1580 cm–1 for Zn(II) are consistent with the formation of carboxylate complexes. The complexes formed offer insight into the degradation processes observed in oil paint films, suggesting that soap formation is rapid when metal ions are solubilized and can occur with unsaturated fatty acids that are present in fresh oils. These complexes may account for the atypical luminescence observed in lead-containing cured oil paint films.

Determining a Structural Distortion and Anion Ordering in La2Si4N6C via Computation and Experiment.

A structural instability in the orthorhombic carbonitridosilicate La2Si4N6C arises when calculating the ab initio phonon dispersion curves. The presence of imaginary modes indicates the compound reported in space group Pnma is dynamically unstable with the eigenvectors showing a monoclinic distortion pathway leading to space group P21/c. Synthesizing La2Si4N6C using a high-temperature route and conducting a co-refinement with high-resolution synchrotron X-ray and neutron powder diffraction shows the predicted peak splitting confirming the predicted lower symmetry crystal structure. Further, the combination of ab initio computation, neutron diffraction, and a total scattering analysis based on a neutron pair distribution function analysis supports that the anions are fully ordered and that carbon is only found on the central position of a star-shaped C(SiN3)4 unit. These results illustrate the power of combining computation and experiment to unequivocally solve crystal structures from polycrystalline powders.

Carrier concentration dependence of structural disorder in thermoelectric Sn1-x Te.

SnTe is a promising thermoelectric and topological insulator material. Here, the presumably simple rock salt crystal structure of SnTe is studied comprehensively by means of high-resolution synchrotron single-crystal and powder X-ray diffraction from 20 to 800 K. Two samples with different carrier concentrations (sample A = high, sample B = low) have remarkably different atomic displacement parameters, especially at low temperatures. Both samples contain significant numbers of cation vacancies (1-2%) and ordering of Sn vacancies possibly occurs on warming, as corroborated by the appearance of multiple phases and strain above 400 K. The possible presence of disorder and anharmonicity is investigated in view of the low thermal conductivity of SnTe. Refinement of anharmonic Gram-Charlier parameters reveals marginal anharmonicity for sample A, whereas sample B exhibits anharmonic effects even at low temperature. For both samples, no indications are found of a low-temperature rhombohedral phase. Maximum entropy method (MEM) calculations are carried out, including nuclear-weighted X-ray MEM calculations (NXMEM). The atomic electron densities are spherical for sample A, whereas for sample B the Te electron density is elongated along the 〈100〉 direction, with the maximum being displaced from the lattice position at higher temperatures. Overall, the crystal structure of SnTe is found to be defective and sample-dependent, and therefore theoretical calculations of perfect rock salt structures are not expected to predict the properties of real materials.

Graphene-Supported Au-Ni Carbon Nitride Electrocatalysts for the ORR in Alkaline Environment

This study reports the preparation and characterization of a new family of electrocatalysts (ECs) for the oxygen reduction reaction (ORR) exhibiting a “core-shell” morphology. The “core” consists of graphene sheets, which are covered by a carbon nitride (CN) “shell” embedding Au and Ni active sites. The investigated ECs are labeled AuNi10-CNl 600/Gr and AuNi10-CNl 900/Gr. The chemical composition and thermal stability are studied by inductively-coupled plasma atomic emission spectroscopy (ICP-AES), elemental analysis and by high-resolution thermogravimetric analysis (HR-TGA). The morphology of the ECs is probed by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and powder X-ray diffraction (XRD). The ORR performance of the ECs is studied both in acid (0.1 M HClO4) and in alkaline medium (0.1 M KOH) by Cyclic Voltammetry with the Thin-Film Rotating Ring-Disk Electrode (CV-TF-RRDE) method. Both ECs exhibit a promising performance in the ORR in the alkaline medium.

Comparison of the Physical Characteristics of Green-Synthesized and Commercial Silver Nanoparticles: Evaluation of Antimicrobial and Cytotoxic Effects

We investigated a novel green route synthesis of silver nanoparticles (AgNPs) using watermelon rind powder extract (WR-AgNPs) as a reducing and capping agent. The efficiency of nanoparticle synthesis was evaluated by comparing the structure, functional groups, antibacterial activity, and cytotoxic effects with commercial AgNPs (C-AgNPs). The AgNP production was initially confirmed based on color changes and wavelength scanning by ultraviolet–visible spectra, which exhibited a surface plasmon resonance peak at 450 nm. We used energy-dispersive spectroscopy to confirm silver and sample purity of both experimental and commercial AgNPs from 2 to 4 keV. Fourier transform infrared spectroscopy analysis showed that the AgNPs were reduced and capped with biomolecules from functional groups in the watermelon powder extract. Further, the analysis showed that the synthesized AgNPs were similar to C-AgNPs. The morphology and crystalline nature of both AgNPs were determined using high-resolution transmission electron microscopy and X-ray powder diffraction. In addition, the synthesized and commercial AgNPs were subjected to antibacterial and cytotoxicity assays. Three-way ANOVA indicated that treatments for WR-AgNPs or C-AgNPs as well as concentration and time had significant effects on Brevibacterium linens and Staphylococcus epidermidis—an odor-causing bacteria. With respect to cytotoxic effects, 67 % cell death was observed with high concentrations (10 mg/L) of both AgNPs.

Synchrotron-based crystal structure, associated morphology of snail and bivalve shells by X-ray diffraction

Synchrotron-based high-resolution X-ray powder diffraction spectra from the body parts of a snail and bivalve (CaCO3), have been recorded with Pilatus area detector. Experiments were performed at Desy, Hamburg, Germany, utilizing the Resonant and Diffraction beamline (P9), with 15keV X-rays (λ=0.82666Å). The external shell of these living organisms, is composed of calcium carbonate, which carries strong biological signal. It consists of some light elements, such as, Ca, C and O, which constitute part of the soft tissue and other trace elements. The knowledge of these diffraction patterns and hence the understanding of structures at molecular level are enormous. The application of synchrotron radiation to powder diffraction is well suited for samples of biological nature via changes in their patterns and also to investigate crystallographic phase composition. With the use of Rietveld refinement procedure, to the high-resolution diffraction spectra, we were able to extract the lattice parameters of orthorhombic polymorph of CaCO3, the most abundant mineral produced by these living organisms. The small size of the crystallite is a very important factor related to the biological structure. The natural model presents a combination of organic and inorganic phases with nanometer size. For the present study, we also used the scanning electron microscopy (SEM) to explore the associated morphology of the snail and bivalve.