Crystal Chemistry Research Articles

A Feasible Dual Modification Strategy of Internal Anion Redox Chemistry and Surface Engineering on P2 Layer-Structured Cathodes in Sodium-Ion Batteries.

Boosting the anion redox reaction opens up a possibility of further capacity enhancement on transition-metal-ion redox-only layer-structured cathodes for sodium-ion batteries. To mitigate the deteriorating impact on the internal and surface structure of the cathode caused by the inevitable increase in the operation voltage, probing a solution to promote the bulk-phase crystal structure stability and surface chemistry environment to further facilitate the electrochemical performance enhancement is a key issue. A dual modification strategy of establishing an anion redox hybrid activation trigger agent inside the crystal structure in combination with surface oxide coating is successfully developed. P2-type layer structure cathode materials with Zn/Li (Na-O-Zn@Na-O-Li) anion redox hybrid triggers and a ZnO coating layer possess superior capacity and cycle performance, along with outstanding structural stability, decreased Mn-ion dissolution effect, and less crystal particle cracking during the cycling process. This study represents a facile modification solution to perform structure optimization and property enhancement toward high-performance layered structure cathode materials with anion redox features in sodium-ion batteries.

Crystal Chemistry and Formation of Authigenic Chlorite: Influence on Tight Sandstone Reservoir in the Yanchang Formation, Ordos Basin, China

Authigenic chlorite is a crucial diagenetic cement that significant impacts tight sandstone reservoirs. The occurrence, crystal chemistry, formation and influences on reservoirs of different authigenic chlorite types were studied in the Yanchang Formation tight sandstones from the Ordos Basin. This study identified two primary types of chlorites: alteration chlorite and autochthonous authigenic chlorite. The alteration chlorite, characterizing by high Fe, Mg, Ti and AlIV contents and low Si and AlVI contents, originated from biotite during diagenesis. The autochthonous authigenic chlorite can be further classified into grain-coating, pore-lining, and pore-filling chlorite. The grain-coating chlorite features thin layers and limited crystal form. During the syndiagenetic stage, Fe2+ and Mg2+ carried by water adsorbed onto the particle surfaces. Additionally, the grain-coating chlorite contains relatively high K content due to the hydrolysis of biotite during the eodiagenetic A stage. The pore-lining chlorite formed during the prolonged eodiagenetic B stage. The biotite and abundant intermediate-basic magmatic fragments released Fe2+ and Mg2+, contributing to the widespread development of euhedral pore-lining chlorite. Notably, the pore-lining chlorite displayed elemental composition variations from the grain edge to the pore center, with increased Fe, Mg and AlIV, and decreased K and AlVI. The pore-filling chlorite formed locally resulted from Fe2+ and Mg2+ crystallization due to the hydrolysis of intermediate-basic magmatic rocks and the dissolution early formed chlorite. The pore-filling chlorite contains the most Fe, Mg and Mn contents and the least K content. Overall, authigenic chlorite acts as a "double-edged sword" in tight sandstone reservoir. The grain-coating and grain-lining chlorite enhance the mechanical strength, resist compaction, and inhibit quartz overgrowth, while pore-filling chlorite trends to obstruct pore throats and break reservoir quality. This study provides valuable insights into the detailed control factors influencing reservoir quality and can serve as a reference for further research.

High temperature structure and vibrational properties of ScXO4 (X= V5+ and P5+): A comparative study

ScVO4 and ScPO4 represent the zircon (xenotime) type structures with smallest trivalent cations, and that enable them to host both transition metal and rare-earth ions for applied optical materials. Thus, their crystal chemistry and thermophysical properties becomes relevance for their application in non-ambient conditions. In this report, high temperature crystal chemistry and vibrational properties of ScVO4 and ScPO4, as observed from in situ high temperature powder XRD and Raman spectroscopic studies, are reported. The comparative analyses of the results indicate that, though both are isostructural, they show drastically different thermal expansion behavior. In case of ScVO4, the c-axis shows significantly larger expansion compared to a-axis, while in ScPO4 the thermal expansion along and a and c-axes are more or less similar. At ambient condition, the thermal expansion anisotropy in ScPO4 and ScVO4 are 1.02 and 3.97, respectively. Additionally, ScPO4 shows relatively lower coefficient of volume thermal expansion compared to ScVO4, (αv = 23.64 × 10−6 K−1 for ScPO4 and 26.09 × 10−6 K−1 for ScVO4), and is contributed by the expansion of ScO8 units in their structures. The thermal expansion coefficients of ScO8 unit in ScPO4 and ScVO4 are 36.3 × 10−6 K−1 and 39.1 × 10−6 K−1, respectively. Temperature evolution of Raman modes indicates weakening of all the modes, except a symmetric stretching mode, with increasing temperature. The anharmonic analyses of the Raman modes indicate that implicit contributions in ScVO4 and ScPO4 are appreciably higher than the explicit contributions, and hence the changes in mode wavenumbers with volume play dominating role in governing their thermal expansion behaviors. Further, it is concluded that ScPO4 is characterized by more or less like rigid unit cell compared to ScVO4.

Crystal chemistry, Raman and FTIR spectroscopy, optical absorption, and luminescence study of Fe-dominant sogdianite

Abstract Fe-dominant sogdianite, a cyclosilicate compound with the chemical formula (Fe3+ 0.74Zr0.64Ti0.46 Al0.15)(□1.02Na0.98)K[Li3Si12O30], was studied. The investigation involved a comprehensive analysis of the mineral sample, including crystal-chemical analysis, Raman and FTIR spectroscopy, optical absorption, and luminescence study. Crystallographic site populations were determined through single crystal structure refinement and electron probe microanalysis. The thermoelastic behavior of a powder was studied using in situ high-temperature X-ray diffraction (30–750 °C). Notably, no phase transition was detected; sogdianite exhibited anisotropic thermal expansion. The first time study of vibrational spectra and spectral bands assigning were performed. The electronic transitions in d 5-ion impurities of sogdianite were studied using optical absorption and luminescence spectroscopy. The origin of pink color and luminescence of sogdianite was clarified. The broad spectral bands in the visible UV spectral region are responsible for the pink color exhibited by sogdianite and could be attributed to d–d transitions occurring in Fe3+ ions.

Novel Tetragonal Boron Pnictides BX (X = N, P, As, Sb, Bi) with Square B2X2 Motifs from Crystal Chemistry and First Principles

Novel tetragonal (P42/mnm) boron pnictides BX (X = N, P, As, Sb, Bi) with chromium boride (crb) topology exhibiting a square B2X2 motif with resulting edge- and corner-sharing tetrahedra were predicted from crystal chemistry and extensively characterized by density functional theory (DFT) calculations. All new BX phases were found to be cohesive with decreasing cohesive energy along the series. Mechanically stable with positive sets of elastic constants, all crb phases exhibit slightly lower hardness than other BX polymorphs due to increased openness of the crystal structures. All-positive phonon frequencies characterize the crb BX family except for X = Bi, which shows a slight acoustic instability; also, the shape of the phonon spectra changes from band-like for X = N, P, As to flat bands for the heavier elements. The electronic band structures reveal insulating to semiconducting properties for crb BX, depending on the pnictogen nature along the series.

Exploring Pyroelectricity, Thermal and Photochemical Switching in a Hybrid Organic‐Inorganic Crystal by In Situ X‐Ray Diffraction

AbstractThe switching behavior of the novel hybrid material (FA)Na[Fe(CN)5(NO)].H2O (1) in response to temperature (T), light irradiation and electric field (E) is studied using in situ X‐ray diffraction (XRD). Crystals of 1 display piezoelectricity, pyroelectricity, second and third harmonic generation. XRD shows that the FA+ are disordered at room‐temperature, but stepwise cooling from 273–100 K induces gradual ordering, while cooling under an applied field (E=+40 kVcm−1) induces a sudden phase change at 140 K. Structural‐dynamics calculations suggest the field pushes the system into a region of the structural potential‐energy surface that is otherwise inaccessible, demonstrating that application of T and E offers an effective route to manipulating the crystal chemistry of these materials. Photocrystallography also reveals photoinduced linkage isomerism, which coexists with but is not correlated to other switching behaviors. These experiments highlight a new approach to in situ studies of hybrid materials, providing insight into the structure–property relationships that underpin their functionality.

Crystal Chemistry and Refined Formula of Tounkite

New data on the crystal structure and isomorphism of extra-framework components in the cancrinite-group mineral tounkite have been obtained using chemical and single-crystal X-ray diffraction data, as well as infrared, Raman, ESR, UV–Vis–near-IR absorption and photoluminescence spectroscopy methods. The crystal structure of tounkite is based on the aluminosilicate framework formed by the САСАСВСВСАСВ stacking sequence with ordered Si and Al atoms The framework hosts Losod and liottite cages as well as columns of cancrinite cages. It is shown that tounkite is characterized by wide variations of the chemical composition. Its simplified crystal–chemical formula is (Na+3.89–5.18K+0.15–1.64Ca2+2.30–2.58(Al6Si6O24)(SO42−,S52−,S4) 2−x (Cl−, HS−)1+y·nH2O (x, y, n < 1). The S2⦁− and S3⦁− radical anions may occur in some tounkite samples in minor amounts. These crystal–chemical features indicate that tounkite crystallizes under highly reducing conditions. All studied tounkite samples were polysynthetic twins. A large 10-layed cage formed at the border between twin components, connected by a rotation of 180° around the [001] axis, which may host the large S52− anion.

Color Tunable Single-phase Cyclosilicate KBaScSi3O9: Eu2+/Tb3+/Sm3+ for n-UV pumped wLEDs

The exploration of stable/efficient phosphor for n-UV chip pumped white light-emitting diodes (wLEDs) remains an arduous task. Herein, a novel series of color tunable Eu2+/Tb3+/Sm3+ tridoped Sc-based cyclosilicate phosphors (KBaScSi3O9: Eu2+/Tb3+/Sm3+) have successfully designed and obtained via facile solid-state reaction based on comprehensive consideration of rigidly structural network of host, weak electron-phonon coupling strength and spectral adjustability of codopants via energy transfer (ET). The crystallographic occupancies of Eu, Tb and Sm primary in Ba/K, Ba and Ba sites in the monoclinic host, respectively were determined on the basis of the Rietveld refinements and crystal chemistry rules. The photoluminescence (PL) properties were systematically investigated in conjunction with structural analyses, implying that the ‘warm’ white light with excellent thermal stability is stemmed from combination of optimized blue (Eu2+), green (Tb3+) and red (Sm3+) emissions via Eu → Tb → Sm ET strategy. Interestingly, Tb ions play both roles of green light luminescent center and ET bridge to achieve cascade ET for connecting Eu/Sm ion pairs because of the adverse metal-metal charge transfer (MMCT) effect (Eu2+ + Sm3+ → Eu3+ + Sm2+). Furthermore, the phosphor-converted wLEDs (pc-wLEDs), by encapsulating the optimal KBS: 4%Eu/4%Tb/6%Sm with commercial n-UV LED chip, show high thermal stability with satisfactory electroluminescence (EL) performances. These results indicate the KBS: Eu/Tb/Sm phosphors are potential candidates for application in high power n-UV pumped pc-wLEDs.

Stoichiometry and topological features of triple molybdates AxByCz(MoO4)n with the heteropolyhedral open MT-frameworks: Synthesis, crystal structure of Rb5{Hf1.5Co0.5(MoO4)6}, and comparative crystal chemistry

In the study of the Rb2MoO4–CoMoO4–Hf(MoO4)2 system a new compound, Rb5Hf1.5Сo0.5(MoO4)6, was obtained, which was synthesized by ceramic technology at 530°С for 80 h in air. Rb5Hf1.5Сo0.5(MoO4)6 single crystals were grown by spontaneous crystallization from a melt solution. Synthesized molybdate melt incongruently at 670 °C. The crystal structure has been refined using single-crystal X-ray diffraction data. Triple molybdate Rb5Hf1.5Сo0.5(MoO4)6 (a = 10.6169(4) Å, c = 38.1282(5) Å. V = 3722.02(2) Å3; space group R3¯c, Z = 6) is characterized by the heteropolyhedral open MT-framework formed by two types of MO6-octahedra and one type of MoO4-tetrahedron. Both MO6-octahedra are predominantly occupied by hafnium with the admixture of cobalt, but characterized by the different ratio between them. Large Rb + cations fill the large cavities and occupy A(1)O9- and A(2)O12-polyhedra. The topological features of the heteropolyhedral open MT-framework in related molybdates with the general formula AxByCz(MoO4)n are discussed.

Exploring Pyroelectricity, Thermal and Photochemical Switching in a Hybrid Organic-Inorganic Crystal by In Situ X-Ray Diffraction.

The switching behavior of the novel hybrid material (FA)Na[Fe(CN)5(NO)].H2O (1) in response to temperature (T), light irradiation and electric field (E) is studied using in situ X-ray diffraction (XRD). Crystals of 1 display piezoelectricity, pyroelectricity, second and third harmonic generation. XRD shows that the FA+ are disordered at room-temperature, but stepwise cooling from 273-100 K induces gradual ordering, while cooling under an applied field (E=+40 kVcm-1) induces a sudden phase change at 140 K. Structural-dynamics calculations suggest the field pushes the system into a region of the structural potential-energy surface that is otherwise inaccessible, demonstrating that application of T and E offers an effective route to manipulating the crystal chemistry of these materials. Photocrystallography also reveals photoinduced linkage isomerism, which coexists with but is not correlated to other switching behaviors. These experiments highlight a new approach to in situ studies of hybrid materials, providing insight into the structure-property relationships that underpin their functionality.

A 5-fold Interpenetrated and Porous Dia-net Metal-Organic Framework Constrcuted from Long and Linear Phenyl-carboxylate Linkers

Interpenetration regulation is of great significance for both the crystal engineering and functional chemistry of MOFs. The combination of long and linear ditopic organic linkers with single or small metal node is effective to produce interpenetration metal-organic framework. Here, a 5-fold interpenetrated and porous dia-net metal-organic framework of [Cd(tpdc)2 ]·3DMF (Cd-MOF, H2 tpdc = 2′,5′-dimethylterphenyl-4,4″-dicarboxylate) was synthesizd under solvothermal reaction, which was structurally characterizaed by single X-ray crystal diffraction, coupled with thermal and luminescence properties study. The compound crystallises in monoclinic P2/c space group with cell parameters of a = 15.7789(4) Å, b = 24.8437(7) Å, c = 26.3720(4) Å, α = 90o , β = 96.5583(19)o , γ = 90o , and V = 23967 Å3 There are 1D channels and porosity of 57.5% for the Cd-MOF, which is a rare example of MOFs with coexistence of high-degree interpenetration and high porosity. The MOF can thermally stable up to 360 o C, with light blue lumiscent emission at 360 nm under a ultraviolet radiation.

Ab-initio calculations, Debye–Wang model and thermodynamic modeling for the short-range order and crystal chemistry characterization of the [formula omitted]8-Al[formula omitted]Fe[formula omitted]Si[formula omitted] solid solution

This paper presents a comprehensive examination of the τ8-Al2Fe3Si4 solid solution, investigating its crystal chemistry and short-range order. To do so, Density functional theory (DFT) calculations were performed, simulating partial substitutions of Al and Si on the four mixed sites of the structure. Our results indicates a negligible contribution from the SRO, allowing the Bragg–Williams approximation to be used to describe its crystal chemistry. Subsequently, systematic substitutions of Al and Si on all mixed sites generated a complete set of ordered structures, called end-members. The formation enthalpies, equation of state and elastic constants for each end-member were calculated, allowing the Gibbs free energy of the solid solution to be derived using the Debye–Wang model. On the basis of this new theoretical insights, a thermodynamic model was developed, predicting the Si occupancy factors in all the mixed sites of the structure at different temperatures, allowing the quantification of its chemical ordering.

Role of zeolite content on the sorption properties of analcime-rich rocks from the Abinky Formation (Niger)

The Abinky formation, composed of analcimolites (i.e., rocks with <70 wt% analcime), underlies Tchirezrine II, which hosts the Imouraren (Niger) uranium deposit. A potential mining project is under consideration to recover U by in situ acid leaching. Analcimolites are uncommon rocks, and assessing their ion-exchange properties is the first step to understand and predict the mobility of aqueous species in these formations. The objective of this study is then to understand the link between the Cation Exchange Capacities (CEC) of analcimolites as a function of their analcime content and associated crystal chemistry. Mineral quantification was performed by Rietveld refinement constrained by local chemical analysis with scanning electron microscopy coupled with Energy Dispersive Spectrometry. CEC were obtained at neutral pH by performing NH4+-for-Na+ exchange (CECNa/NH4), and Na+/H+ ion exchange experiments were performed with 4 analcimolites.Results showed that the analcime crystal chemistry deduced from Rietveld refinement was in good agreement with that obtained from SEM analysis (1.99 < Si/Al < 2.53). The results showed that all samples had a positive correlation between CECNa/NH4 and analcime content until ~30 meq/100 g for a sample containing ~85wt%Riet. of analcime, and that ~6 % of the total amounts of Na+ present in the analcime could be exchanged by NH4+ and H+. Based on Si and Al aqueous measurements, results showed that exchange with Na+ is the main process consuming H+ during Na+/H+ exchange when pH > 3.5. These experimental data were then interpreted by considering a single site equal to the CECNa/NH4 value, specific for each analcimolite, and a selectivity coefficient equal to log KNa/H = 1.3 (Gaines Thomas convention) being equal for all samples investigated. Finally, these data were used to assess the role played by Na+/H+ exchange in the pH evolution of the pore water of an analcime-rich rock subjected to dynamic acidification.

Room-temperature NH3 sensor based on CoFe2O4/PANI composite with porous structure

Development of chemo-resistive room-temperature ammonia (NH3) sensor with high performance remains a great challenge to this day. In this paper, we demonstrate a room-temperature NH3 sensor based on organic-inorganic cobalt ferrite (CoFe2O4)/polyaniline (PANI) composite. The CoFe2O4 porous nanosheets were firstly prepared by using a direct precipitation method, and then the PANI were anchored onto the surfaces of the CoFe2O4 porous nanosheets through an in-situ polymerization process to form the CoFe2O4/PANI composite. The crystal structure, morphology, and surface chemistry of the CoFe2O4/PANI composite were characterized by combined techniques of X-ray diffraction, electron microscopy, and spectroscopy. Due to the porous feature of the composite and the formation of p-p heterojunctions between the CoFe2O4 and PANI, the CoFe2O4/PANI gas sensor exhibited excellent NH3-sensing performance with high response (13 to 100 ppm NH3), good selectivity, wide detection range (10–500 ppm), and rapid response/recovery rate (18/31 s to 100 ppm NH3) at room temperature. Additionally, the CoFe2O4/PANI gas sensor owned outstanding repeatability and long-term stability. This study offered a promising candidate of CoFe2O4/PANI composite for constructing room-temperature NH3 sensor.

Synthesis and characterization of (Pb1−x Sr x )MnBO4: a structural and spectroscopic study

Abstract The presence of ns 2 stereo-chemical active lone electron pairs (LEPs) causes asymmetric atomic environments around a given p-block cation, leading to change the crystal chemistry of a respective system. Here we report a series of mullite-type compounds to understand at what extend Sr2+ replaces the stereochemical active Pb2+ cation in (Pb1−x Sr x )MnBO4. Each member of the solid solution has been synthesized by conventional solid-state method. The polycrystalline samples are characterized using X-ray powder diffraction followed by Rietveld refinement. Substitution of Pb2+ with Sr2+ leads to contraction of the a lattice parameter with slight elongation in the b and c direction. For a difference of 1 pm of the ionic radius between Sr2+ and Pb2+, the cell volume contracts about 4 % between the end members as the spatial requirement of the LEP activity in the MBO4 2− channels significantly decreases. Within the solid solution, two distinct Pb/Sr–O2 bond distances significantly differ, which gradually decreases with increasing strontium content leading to a more symmetric coordination around strontium. The calculated BVS of Pb2+/Sr2+ exhibits a linear correlation with the Wang–Liebau eccentricity parameter, indicating to an increased bonding ability cation. The vibrational properties are characterized by both Raman and FTIR spectroscopy, complementing the XPRD results. Electronic band gaps of selected (Pb1−x Sr x )MnBO4 samples were obtained from diffuse reflectance spectroscopy data. Additionally, the Sr containing samples show higher thermal stability than the Pb containing counterparts.

From quartz (qtz) to diamond (dia) carbon topologies: Stepwise rationale from crystal chemistry and DFT investigations

From crystal chemistry and density functional theory DFT calculations, a stepwise rationale is proposed for the transformation from standalone distorted tetrahedron α-C5favored over standalone regular tetrahedron β-C5to high density – ultra hard orthorhombic α-C6and β-C6withqtz(quartz-based) topology characterized by 3D arrangements of distorted tetrahedra to lower densitydia-C topology (diamond-like, with regular C4 tetrahedra). Progressive C insertions into orthorhombic α-C5, α-C6, and lastly into C7were operated leading to ultimate C8stoichiometry identified as diamond-like. C7was also used as template to devise C3N4carbonitride with exceptional mechanical properties. The induced structural and physical changes are supported with elastic properties pointing to ultra-hardness, larger forqtzα,β-C6thandiaC8and inferred dynamic stability for all stoichiometries from the phonons band structures. The thermodynamic quantities as the specific heat were compared with diamond experimental CV. The electronic band structures reveal semi-conducting C6, metallic C7characterized by diamond-defect structure, and insulating C8. The results are meant to help further systemic understanding of tetrahedral carbon allotropes.

The local state of hydrogen atoms and proton transfer in the crystal structure of natural berborite, Be2(BO3)(OH)‧H2O: Low-temperature single crystal X-ray analysis, IR and 1H NMR spectroscopy, and crystal chemistry and structural complexity of beryllium borates

Beryllium borates are mostly water-free, with the natural mineral berborite, Be2(BO3)(OH)‧H2O, being the only known exception. A sample of berborite from the Vevja quarry, Tvedalen, Larvik, Norway was studied by single-crystal X-ray diffraction, variable temperature 1H nuclear magnetic resonance (NMR), and infrared (IR) spectroscopy. The crystal structure is the trigonal 1T-polytype with space group P321 and is based on electroneutral [BeØ2(BΔO3)]-layers formed by BeO3Ø-tetrahedra and BΔO3-triangles. Due to statistical occupancy of the Ø-ligand by hydroxyl groups (50%) and water molecules (50%), berborite-1T and its related polytypes are characterized by complex systems of hydrogen bonds. Accurate analysis shows that in the structure of berborite there are two independent systems of hydrogen bonds involving mobile protons. Lowering of temperature results in the complete stabilization of protons at the critical “freezing-point” of 243 K. The crystal chemistry and complexity of layered beryllium borates are discussed. Despite the broad structural diversity of these compounds, their crystal structures are classified as simple (20–100 bits per unit cell) or intermediately complex (100–500 bits per unit cell). The complexity of berborite polytypes increases in accordance with the quantity of layers from 29.038 (1T) to 78.077 (2H), which is in good agreement with the negative contribution of complexity to the configurational entropy.

Revealing the role of crystal chemistry in REE fractionation in skarn garnets: insights from lattice-strain theory

Revealing the role of crystal chemistry in REE fractionation in skarn garnets: insights from lattice-strain theory

Crystal chemistry of the solid solutions based on β-Mn

Binary solid solutions based on β-Mn have been systematically investigated from a structural point of view. The site occupancies of the substitutional solute elements Al, Co, Fe, In, Ir, Ni, Os, Ru, Si, Sn and Zn on the two distinct sites of its crystal structure have been determined experimentally by Rietveld refinement of X-ray or neutron powder diffraction data. The atomic distribution is discussed in light of the changes of lattice parameters in the solution and compared between the different chemical systems. A systematic analysis of the volume change within the complete binary systems has been carried out. Anomalies are observed and explained for the time, by assuming that Mn presents two different atomic radii at its two different sites. This feature is unique in metallic solid solutions in the absence of any mixed valence. The study is complemented by a detailed DFT investigation of the different systems demonstrating an anomaly with the description of the Mn atom by traditional first-principles calculations. This problem leads to miscalculation of the lattice parameter of pure Mn and, as a consequence, of the site occupancies in the binary systems. The importance of the ordering of the solute element for the Calphad modeling is discussed and the use of a two sublattice model for the description of β-Mn solid solutions in agreement with the presence of two different Wyckoff positions, instead of the conventional disordered solution model, is highly recommended.

Fabrication, defect chemistry and microstructure of Mn-doped UO2

Mn-doped UO2 is under consideration for use as an accident tolerant nuclear fuel. We detail the synthesis of Mn-doped UO2 prepared via a wet co-precipitation method, which was refined to improve the yield of incorporated Mn. To verify the Mn-doped UO2 defect chemistry, X-ray absorption spectroscopy at the Mn K-edge was performed, in addition to X-ray diffraction, Raman spectroscopy and high-energy resolved fluorescence detection X-ray absorption near edge spectroscopy at the U M4-edge. It was established that Mn2+ directly substitutes for U4+ in the UO2 lattice, accompanied by oxygen vacancy (Ov) charge compensation. In contrast to other divalent-element doped UO2 materials, compelling evidence for U5+ in a charge compensating role was not found. This work furthers understanding of the structure and crystal chemistry of Mn-doped UO2, which could show potential advantages as a novel efficient advanced nuclear fuel.