Crystal Chemistry Research Articles

Abstract Bastnäsite (REECO3[F, OH]) is a critical mineral in carbonatitic rare earth element (REE) deposits and serves as a primary global source of REEs. Understanding its crystal chemistry and thermodynamic properties is essential for modeling REE mobilization and deposition in various geological processes. Despite the complexity in natural bastnäsite—arising from cationic substitutions among REE species and coupled F-OH substitution—the impacts of F-OH substitution on its crystal structure and thermodynamic properties remain poorly constrained. In this study, we systematically investigate a synthetic bastnäsite-hydroxylbastnäsite (Bsn-Ce – Hbsn-Ce; CeCO3F-CeCO3OH) solid solution series using single-crystal X-ray diffraction and Raman spectroscopy. Notably, this is the first study to reveal: (1) the positions of hydrogen atoms in bastnäsite and hydroxylbastnäsite, as well as the order-disorder transition of hydrogen initiated by F-OH substitution in hydroxylbastnäsite, which explains the discrepancies in Raman spectroscopy between synthetic end-members and natural hydroxylbastnäsite; (2) the phase boundary between bastnäsite and hydroxylbastnäsite, with crystal structural data indicating a phase boundary at F = 0.41–0.52 apfu; and (3) the effect of F-OH substitution on the volume of the Bsn-Ce – Hbsn-Ce solid solution. This study is also the first attempt to establish a quantitative framework for describing the volume-composition behavior of incomplete solid solutions involving F-OH substitution. Furthermore, this study provides a foundational understanding of the crystal chemistry necessary for further investigations into the thermodynamic properties of Bsn-Ce – Hbsn-Ce solid solutions.

Occurrence, Crystal Chemistry and Morphology of Erionite from New Zealand

Synthesis, crystal chemistry, spectroscopic characterization, and topological features of anhydrous barium bromide and iodide thiocyanates, BaX(SCN) (X = Br, I)

Molecular, Crystal, and Surface Chemistry of <i>p</i> -Aminobenzoic Acid and the Interrelationship between Its Solution-Phase Crystallization and Solid-Form Selectivity: A Review

Abstract. A series of 17 museum tourmaline samples from several pegmatites of Minas Gerais, Brazil, were investigated by several techniques including single-crystal X-ray structure refinements, electron microprobe, and laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS). Chemically, most samples are Na-dominant on the X site and therefore belong to the alkali group. They correspond to fluor-elbaites or elbaites, where similar proportions of Al and Li share the Y positions. Elbaites are located close to the elbaitic end-member, with Fe2+ strongly depleted and the schorlitic component negligible, while fluor-elbaites tend to align along the fluor-elbaite to fluor-schorl solid solution. One sample, with vacancies dominant on the X site, is identified as a rossmanite close to the foitite compositional field. Besides the classical schorlitic substitution, several other mechanisms were observed, evolving towards rossmanite (XNa++0.5YLi+=X□+ 0.5 YAl3+), towards liddicoatite (XNa++0.5YAl3+=XCa2++0.5YLi+), or towards oxy-foitite (0.5 XNa++YFe2++0.5W(OH)-=0.5X□+YAl3++0.5WO2−). Single-crystal data indicate a unit-cell parameters varying between 15.8187(3) and 15.9309(3) Å and c parameters ranging from 7.0924(2) to 7.1279(2) Å. These values are similar to those obtained for Brazilian tourmalines of the elbaite–schorl solid solution. A detailed cation distribution has also been established, indicating that the B site is fully occupied by boron, that the T site is mainly occupied by Si and sometimes by minor amounts of B, and that the Z site is mainly occupied by Al with sometimes minor amounts of Fe3+. The X site contains vacancies, Na, K, and Ca, and the Y site is occupied by Li, Al, and Fe2+ and minor amounts of Mn2+, Ti, Mg, and Zn. In two samples, a significant disorder between Li and Ca on the X and Y sites has been observed. The position of our samples in a diagram correlating the fluorine and the Fe2+ contents of tourmalines indicates that they are below the trend admitted for primary pegmatitic tourmalines. This feature can be explained by their occurrence in miarolitic cavities, where fluid circulations may affect the tourmaline composition. Finally, the trace-element contents, including rare earth elements (REEs), are discussed in detail and appear to be influenced by both the geochemical pegmatitic context and crystal–chemical constraints.

Perovskites—materials adopting or derived from the ABX₃ structural archetype—have progressed from classical oxide ferroelectrics and superconductors to today’s halide-based optoelectronics, catalysis, and Ionics. This chapter surveys crystal chemistry and structure–property relationships across oxide and halide families; defect physics and ion transport; synthesis and microstructure control from bulk to nanocrystals and 2D phases; and device-level advances in photovoltaics, light emission, sensing, catalysis, solid-state Ionics, and beyond-CMOS electronics. We also review stability pathways, lead-free strategies, environmental and sustainability considerations, characterization toolkits, and computational discovery. Emphasis is placed on how fundamental mechanisms—tolerance factor, octahedral tilts, soft lattices, defect tolerance, excitonic effects, and dynamic disorder—enable rapid translation from lab to technology.

Novel group IVA (A) equiatomic hexagonal nitrides A4N4 (A = C, Si, Ge) with characteristic {A2N2} layered tetrahedra: Crystal chemistry and first-principles calculations

Lithium indium chloride, Li3InCl6, is a promising solid-state electrolyte for all-solid-state batteries (ASSBs) due to its high room-temperature ionic conductivity and electrochemical stability. However, its sensitivity to atmospheric moisture leads to the formation of stable crystalline hydrates, which significantly affect both its electrochemical performance and crystal chemistry. In this study, temperature- and time-dependent in situ X-ray diffraction was employed to investigate the underlying mechanisms governing the hydration and dehydration processes of Li3InCl6 and its hydrated counterpart, Li3InCl6·xH2O (x > 2), by monitoring the associated structural transformations. The study reveals a two-step phase transition between the hydrated and dehydrated phases, with the identification of an intermediate phase, Li3InCl6·yH2O (1.5 < y < 2). Coupled Rietveld refinements of X-ray and neutron powder diffraction data elucidate the crystal structure of this intermediate hydrate, providing crucial insights into the reversible reaction mechanism of Li3InCl6. Understanding these hydration and dehydration processes is vital for optimizing the electrochemical performance and stability of Li3InCl6 in ASSBs applications.

Carbonate minerals such as calcite cover a significant portion of Earth's ice-free land surface. Beyond their widespread distribution, they play a critical role in geological processes, including the global carbon cycle and various biogeochemical processes. Understanding the crystal chemistry of carbonates is therefore essential for advancing our knowledge of these systems. Atom probe tomography offers promising potential for revealing nanoscale chemical and isotopic processes in minerals; however, its application to carbonates remains technically challenging due to their poor thermal conductivity and absorption. In this study, we apply and adapt an in situ metallic coating technique and optimize atom probe tomography acquisition parameters for calcite. The results demonstrate that applying a Cr coating to calcite specimens significantly improves experimental yield and enhances mass resolution during atom probe analysis. Despite these improvements, the data do not yield stoichiometric proportions for calcite due to the post-ionization dissociation of CxOy molecules into neutrals. These findings provide a framework for extending atom probe tomography methods to other poorly conducting or beam-sensitive materials.

Abstract The structure of Na3[UO2F5] (I) and CaRb4[UO2F4]3⋅3H2O (II) crystals was studied using X-ray diffraction analysis. The uranium-containing structural units are pentagonal bipyramids [UO2F5]3−, which are isolated from each other in I and linked by bridging fluorine atoms into trinuclear complexes of the composition [(UO2)3F12]6− in II. The latter one fills the existing gap in the crystal chemistry of uranyl fluorides and oxofluorides by representing the first example of a trinuclear complex, while di-, tetra- and pentanuclear complexes have been observed before. The first compound has been known for more than half a century, although here we present the first report on its crystal structure. The crystal chemical formulae of the uranium-containing complexes in I and II are AM 1 5 and A 3 M 2 3 M 1 9, where A = UO2 2+, М 2 and М 1 = F−. In both structures, the uranyl-containing complexes are linked into 3D frameworks by R–F and R–O coordination bonds with outer-sphere R cations (R = Na, Rb or Ca). As both compounds I and II turned out to be non-centrosymmetric their ability to generate the second harmonic was theoretically predicted based on parameters of Voronoi–Dirichlet polyhedra. Experimental verification of the obtained values is of undoubted interest.

Abstract Ceramic electrolytes (CEs) offer high ionic conductivity and exceptional stability for improving performance and safety in solid‐state sodium metal batteries (SSMBs). However, inevitable defects and disorders in polycrystalline materials pose challenges in understanding ion transport and failure mechanisms within CEs. Addressing these issues requires decoupling the complex ionic dynamic processes. Herein, Na3Zr2Si2PO12 (NZSP) CEs are prepared with varying defect concentrations and crystal chemistry by NaF addition, and conducted both qualitative and semi‐quantitative analyses to diagnose their failure evolution upon electrochemical cycling with metallic sodium electrodes. Dynamic characterizations reveal the correlation between relaxation behavior and atomic interactions in the amorphous interphase at grain boundaries. Furthermore, two models are proposed to describe the failure evolution of CEs: one dominated by dendrite growth and the other dominated by solid‐electrolyte interphase (SEI) formation during sodium plating/stripping. In the latter model, the SEI relaxation distribution function (γSEI) derived from the distribution of relaxation times (DRT) analysis, assessed by electrochemical impedance spectroscopy, serves as a criterion for determining and predicting the direction of failure evolution. This work provides new insights into failure evolution mechanisms of CEs and demonstrates the effectiveness of DRT‐based diagnosis for optimizing solid‐state sodium metal batteries.

Transition‐metal di‐pnictides and di‐chalcogenides of the pyrite‐marcasite family are model systems for crystal chemistry. Phase formation and stability of transition‐metal di‐antimonides in the orthorhombic marcasite structure are investigated. A two‐step synthesis of granular films, comprised of combinatorial deposition of the transition metal and subsequent antimonization at different temperatures, is employed. This technique allows to efficiently and quickly explore the possible ranges of substitution and evolution of lattice parameters within the marcasite structure. In particular, the formation and crystal structures of the (Fe,Ni)Sb2 and the (Fe,Cr)Sb2 substitution series are investigated. Continuous substitution of FeSb2 (class‐A marcasite) with Ni up to Fe0.5Ni0.5Sb2, and the clear phase separation between Fe0.5Ni0.5Sb2 and a Ni‐rich Ni1−zFezSb2 phase (class‐B marcasite) is evidenced. Cr‐substituted FeSb2 shows a subtle phase separation into a Fe‐rich Fe1−yCrySb2 and a Cr‐rich Cr1−zFezSb2‐phase (both class‐A marcasite) when synthesized at 500 °C. At a slightly higher synthesis temperature of 540 °C, the continuous substitution of Fe by Cr in FeSb2 is possible. These results represent an example for the agility of combinatorial deposition of thin films in exploring phase diagrams of transition‐metal di‐pnictides as a unique tool to study this broad material family.

This study investigates how l-glutamic acid (Glu) behaves in water and in aqueous solutions of tetrapropyl bromide (TPAB) and tetrabutyl bromide (TBAB) across temperatures from 293.15 to 313.15 K. Using volumetric methods, researchers measured solution densities and derived parameters like apparent and partial molar volumes, molar expansibility, Hepler’s constant, and transfer volume to analyze ion–on and ion–solvent interactions. The rise in partial molar volume ({V}_{phi }) with increasing molality of Glu indicates stronger solute–solvent interactions as the concentration of amino acids in the solution grows, The positive and increasing values of {V}_{phi }^{0} with temperature and TPAB/TBAB concentration suggest enhanced ion–solvent and hydrophilic interactions, indicative of stronger electrostrictive effects. The interaction analysis revealed that the ion–ion, ion–hydrophilic, and hydrophilic–hydrophilic forces between the zwitterionic centers {(-text{COO}}^{-} and {-text{NH}}_{3}^{+}) and the polar groups of Glu (-text{COOH} and {-text{NH}}_{2}), as well as the ions in aqueous TPAB text{and} TBAB, are significantly stronger and dominate over the hydrophobic interactions involving the nonpolar organic segments of the amino acid and TPAB/TBAB. These findings have wide-ranging applications, from improving pharmaceutical formulations and drug delivery systems to advancing biochemical research on amino acids in complex environments. They also offer valuable insights into solute–solvent interactions, promoting greener, energy-efficient industrial processes and supporting global sustainability efforts. Moreover, by linking these molecular insights to practical applications in crystallization, polymer design, and environmental chemistry, the current study bridges fundamental science with real-world relevance marking a clear advancement over prior literature.

Phenazines, otherwise known as dibenzo-annulated pyrazines, are a unique class of tricyclic organic molecules. They are chemically stable and highly aromatic due to their extended conjugation. Along with their biomedicinal significance, phenazines often play a major role in manipulating the optical as well as electrical properties of organic semiconductors. The planar structure in the heterocyclic aromatic phenazines and their natural inclination to form stacked columns due to the π-π interactions between two consecutive molecules have made them quite a suitable moiety for the formation as well as extension of the core part of discotic liquid crystals (DLCs). Theirefficient charge-carrying ability makes them well-suited for organic electronic materials. Furthermore, their properties can be fine-tuned with simple chemical changes, rendering them appropriate for many advanced applications. This review focuses on the chemistry of phenazine-based DLCs and their significance in optoelectronic applications.

This study examined the eco-friendly synthesis of zinc oxide (ZnO) nanoparticles using Cladophora glomerata extracts as reducing and stabilizing agents, comparing zinc acetate and zinc chloride precursors for biomedical and environmental applications. Zinc acetate-synthesized ZnO nanoparticles showed a significant absorption peak around 320–330 nm, indicating stable, quasi-spherical ZnO nanoparticles with a narrow size distribution, primarily around 100 nm. Zeta potential measurements revealed a value of −25 mV for these particles, suggesting moderate colloidal stability. XRD analysis confirmed a highly crystalline hexagonal wurtzite structure for zinc acetate-derived ZnO, and SEM images supported a proper microstructure with approximately 2 µm particle size. FTIR analysis indicated higher-quality ZnO from zinc acetate due to the absence of moisture and hydroxyl groups. Conversely, zinc chloride-derived ZnO particles displayed a broader absorption spectrum around 370 nm, indicative of significant aggregation. Their narrower zeta potential distribution around +10 mV suggested diminished colloidal stability and a heightened aggregation tendency. While a peak around 100 nm was observed, many particles exceeded 1000 nm, reaching up to 10,000 nm. XRD results showed that zinc chloride adversely affected crystallinity, and SEM analysis indicated smaller particles (approx. 1 µm). FTIR analysis demonstrated that zinc chloride samples retained hydroxyl groups. Both zinc acetate- and zinc chloride-derived ZnO nanoparticles produced notable inhibitory zones against Gram-positive (L. monocytogenes, S. aureus) and specific Gram-negative bacteria (E. coli, K. pneumoniae). Zinc acetate-derived ZnO showed a 21 mm inhibitory zone against P. vulgaris, while zinc chloride-derived ZnO showed a 10.1 mm inhibitory zone against C. albicans. Notably, zinc chloride-derived ZnO exhibited broad-spectrum antimicrobial activity. MIC readings indicated that zinc acetate-derived ZnO had better antibacterial properties at lower concentrations, such as 3.125 µg/mL against L. monocytogenes. These findings emphasize that the precursor material selection critically influences particle characteristics, including optical properties, surface charge, and colloidal stability.

Blue quartz phenocrysts are encountered in felsic rocks and their metamorphosed equivalents. Despite their occurrence, detailed investigations into their crystal chemistry and mineralogical properties remain limited. This study focuses on a multiscale characterization of blue quartz phenocrysts hosted in metarhyolites from the Rio dos Remédios Group (Paramirim Aulacogen), one of the notable occurrences of blue quartz in Brazil. The mineralogy of the host rock was analyzed using optical petrography, bi-polished plates, and powder X-ray diffraction. Advanced techniques, including electron probe microanalysis (EPMA), infrared (IR) spectroscopy, and scanning and transmission electron microscopies, were employed to examine trace elements, OH-related defects, and inclusions in quartz grains. Additionally, electron paramagnetic resonance (EPR) was used to investigate coarse and fine powders of blue and colorless quartz phenocrysts. The study provides detailed insights into the crystal chemistry and microscopic properties of Rio dos Remédios quartz phenocrysts, highlighting Fe- and Ti-rich inclusions exsolved into the quartz matrix as the main distinction between blue and colorless regions. OH-related defects, grain size, and aspect ratio distributions were similar between the two varieties. These findings contribute to a better understanding of the mineralogical and chemical factors influencing the properties of blue quartz phenocrysts.

Mathematical crystal chemistry views crystal structures as the optimal solutions of the mathematical optimization problem formalizing inorganic structural chemistry. This paper introduces the minimum and maximum atomic radii depending on the types of geometrical constraints, extending the concept of effective atomic sizes. These radii define permissible interatomic distances instead of interatomic forces, constraining feasible types and connections of coordination polyhedra. The definition derives the continuous optimization problem as dense packings of flexible atomic spheres. Additionally, discrete variables and constraint functions, which give a choice of creatable types of geometrical constraints depending on the spatial order of atoms, are implemented to formalize the feasible atomic environment, such as the composition of coordination polyhedra, resulting in acceleration of structure search and decrease of the number of local minima. The framework identifies unique optimal solutions corresponding to the structures of spinel, pyrochlore (α and β), pyroxene, quadruple perovskite, cuprate superconductor YBa2Cu3O7−x, and iron-based superconductor LaFeAsO. Notably, up to 95% of oxide crystal structure types in the Inorganic Crystal Structure Database align with the optimal solutions preserving experimental structures despite the discretized feasible atomic radii. These findings highlight the role of mathematical optimization problems as a theoretical foundation for mathematical crystal chemistry, enabling efficient structure prediction.

Crystal chemistry and isomorphism of high-calcium eudialyte-group minerals from the Tamazeght peralkaline complex, Morocco

Metal chalcophosphates have extensive applications in numerous frontier scientific fields due to their rich structures. Herein, six novel quaternary thiophosphates (MIIxEu1-x)2P2S6 (MII = Ca, Sr, Ba, and Pb), viz. (Ca0.48Eu0.52)2P2S6 (1), (Sr0.59Eu0.41)2P2S6 (2), (Ba0.49Eu0.51)2P2S6 (3), (Pb0.60Eu0.40)2P2S6 (4), (Ba0.21Eu0.79)2P2S6 (5), and (Ba0.73Eu0.27)2P2S6 (6), were synthesized by the flux-assisted boron-sulfur solid-state reactions. They crystallize in the monoclinic P2/1n space group, and their three-dimensional polyanionic frameworks are constructed by MII/EuSx polyhedra and P2S6 dimers. The crystal chemistry of 1-6 is systematically analyzed, and the effects of cation partial substitution and co-occupation on the local structure and electronic structure are studied. The optical band gaps and birefringences of 1-6 are in the ranges of 2.04 ∼ 2.64 eV and 0.06 ∼ 0.09, respectively, and they exhibit ferromagnetism or antiferromagnetism. 4 shows a significant photocurrent response (56.43 μA/cm2). This work enriches the chemistry of rare-earth chalcophosphates and gives some hint for their further development.

ABSTRACTMetasomatic fluids are thought to be oxidising agents that react with the surrounding mantle rocks, causing changes in the bulk Fe3+/ΣFe, their redox state, and affecting the partitioning of trace elements and the fractionation of O isotopes. Worldwide distributed metasomatized peridotites represent the ideal case study to investigate the role that crystal chemistry has on the O‐isotope fractionation. We present mineral‐chemical data of mantle peridotites from Tallante (Spain) such as major and trace elements, oxygen fugacity, and O‐isotope data. Our results show that the O‐isotope composition of volumetrically minor spinel in the residual mantle can be significantly affected by the oxidising metasomatic melts or fluids, likely implying that the oxidation of Fe2+ to Fe3+ favours 18O uptake in spinel structure with respect to 16O.