Nominal Stoichiometry Research Articles

Microstructural, magnetic, dielectric, and optical studies of La‐doped Sr2Fe0.5Hf1.5O6 double perovskite oxides

AbstractHerein, we report on the structural, magnetic, dielectric, and optical properties of La‐doped Sr2‐xLaxFe0.5Hf1.5O6 (SLFHO, 0.0 ≤ x ≤ 2.0) double perovskite oxides synthesized by solid‐state reaction method. X‐ray powder diffraction data and their Rietveld refinement reveal that the SLFHO powders crystallize in an orthorhombic structure with the Pnma space group. The SLFHO powders exhibit spherical morphology with an average particle size of 160 nm, as shown from SEM images. Their molar ratios of the Sr:La:Fe:Hf elements were determined as 1.77:0.50:0.50:1.95 by energy dispersive X‐ray spectroscopy data, approaching their nominal stoichiometry. X‐ray photoelectron spectra verified that Sr2+, La3+, Fe3+, and Hf4+ (Hfx+) ions existed in the SLFHO powders, and oxygen existed in species lattice oxygen and adsorbed oxygen, respectively. The SLFHO powders exhibit ferromagnetic behavior at 2 and 300 K, respectively, and at 2 K the saturated magnetization was 5.66 emu/g (or 0.60 μB/f.u.). Magnetic transition temperature, TC was determined to be 867 K. Dielectric measurements demonstrated a strong frequency‐dependent dielectric behavior observed in the SLFHO ceramics and a relaxor‐like dielectric behavior appearing in the temperature range of 200–600 K. Such relaxor‐like dielectric behavior is ascribed to the dielectric response of the singly‐ionized oxygen vacancies ( an activation energy of 0.54 eV. Room temperature optical properties of the SLFHO powders examined by using UV–vis diffuse reflectance spectroscopy exhibit high optical absorption in this wavelength region, and a wide indirect optical bandgap (Eg = 3.39 eV) was estimated using the Tauc's relation from the diffuse reflectance spectra. The SLFHO double perovskite oxides display high‐temperature ferrimagnetism, relaxor‐like dielectric behavior, and wide optical bandgap, making them potential to be employed in the fields of high‐temperature spintronics and magnetic semiconductor devices.

A DFT Computational Study of Type-I Clathrates A8Sn46-x (A = Cs or NH4, x = 0 or 2).

Semiconducting clathrates have attracted considerable interest in the field of thermoelectric materials. We report here a computational study on the crystal structure, the enthalpy of formation, and the physical properties of the following type-I clathrates: (a) experimentally studied Cs8Sn44 and hypothetical Cs8Sn46 and (b) hypothetical (NH4)8Sn46-x (x = 0 or 2). The ab initio VASP calculations for the nominal stoichiometries include the geometry optimization of the initial structural models, enthalpies of formation, and the electronic and phonon density of states. Comparison of the chemical bonding of the structural models is performed via the electron localization function. The results show that the presence and distribution of defects in the Sn framework for both Cs8Sn46-x and (NH4)8Sn46-x systems significantly alters the formation energy and its electrical properties, ranging from metallic to semiconducting behavior. In particular, one defect per six-membered Sn ring in a 3D spiro-network is the thermodynamically preferred configuration that results in the Cs8Sn44 and (NH4)8Sn44 stoichiometries with narrow-band gap semiconducting behavior. Moreover, the rotation of the ammonium cation in the polyhedral cavities is an interesting feature that may promote the use of ammonium or other small molecular cations as guests in clathrates for thermoelectric applications; this is due to the decrease in the lattice thermal conductivity.

Mössbauer study of iron oxide nanoparticles

AbstractMagnetic nanoparticles have recently attracted attention for biochemical and medical applications like drug delivery and hyperthermia for a variety of reasons with most important being their stability, chemical compatibility, and suitable magnetic properties like moderate specific mass magnetization. Cobalt ferrites are a well‐studied family of materials and the partial substitution of Fe3+ cations by rare earth (RE) ones may be used to tune the magnetic properties. In the present work pure and substituted Co ferrite nanoparticles with nominal stoichiometry CoFe2−xRxO4 (R = Yb, Gd; x = 0.05, 0.1, 0.3) synthesized by the co‐precipitation method are studied with 57Fe Mössbauer spectroscopy to determine the incorporation of RE ions in the spinel lattice. The fitting procedure was based on the standard spinel model using two sextets for the octahedral and the tetrahedral coordinated positions of Fe atoms. All isomer shift values were found within the typical range of high spin ferric ions while quadrupole splitting values strongly suggest that there is a substitution preference; RE ions replace iron ones in octahedral sites. The inversion parameter was found to decrease with RE content (lowest value about 0.534 for CoFe1.90Yb0.10O4) and thermal treatment always results in changing the material toward normal spinel, while pure CoFe2O4 was inverse. Thermal treatment of substituted materials in ambient air at temperature range 1500–1700 K for 12 h increase crystallite size and changes the degree of inversion.

Thermostructural evolution of boron carbide characterized using in-situ x-ray diffraction

Boron carbide, with a nominal stoichiometry of B4C, is a highly desired ceramic candidate for armor applications due to its high hardness derived from the complex crystal structure. However, stress-induced local amorphization can lead to failure and is a known challenge for this material which must be addressed for applications in ballistic environments. Understanding boron carbide's atomic structural behavior and bonding environment is critical in determining effective strategies to mitigate these issues. In this work, the thermo-structural behavior of B4C has been studied in detail using a conical nozzle levitator system coupled with in-situ synchrotron X-ray diffraction. Lattice expansion and the resulting thermal expansion coefficients (CTEs) were determined from 25-2100 °C. Rietveld refinements showed anisotropic atomic displacement for each of the 4 unique sites as a function of temperature. An exceptionally large z-axis displacement for the boron chain center is linked to bond weakness and may be linked to faα11ster expansion of the α33 relative to CTEs. Thermally induced lattice changes can inform the use of boron carbide at elevated temperatures as well as help develop strategies for mitigating structural failure for armor applications.

Dissolution of Nb-doped hydroxyapatite prepared via low-temperature mechanochemical method: Spectroscopy studies

Calcium phosphate glass ceramics with nominal hydroxyapatite stoichiometry doped with niobium were synthesized using simple as well as low-temperature mechanochemical method and then in the form of compressed pellet were submitted to the static dissolution process in distilled water for one month. The results of structural analysis, performed mainly on the base of spectroscopic methods such as: infrared absorption spectroscopy, energy-dispersive X-ray spectroscopy, photoelectron spectroscopy as well as soft and tender X-ray absorption spectroscopies, indicate that during the dissolution process the presence of niobium reduced the dynamics of the calcium phosphate new layer formation, without a significant impact on the morphology and stoichiometry of this layer. Moreover, the Nb addition favored the formation of hydroxyapatite and Ca-deficient hydroxyapatite, both during the synthesis and dissolution processes, and facilitated the incorporation of the CO3-2 groups into the ceramic matrix, leading to the formation of B-type carbonated apatite.

Vacancy ordering in zirconium carbide with different carbon contents

Zirconium carbide (ZrCx) ceramics with different carbon contents were prepared by reactive hot-pressing. The rock-salt structure of ZrCx was the only phase detected by x-ray diffraction of the hot pressed ceramics. The relative densities of ZrCx decreased as carbon content increased, in general. The actual carbon contents were measured by completely oxidizing the ZrCx ceramics to ZrO2. For most compositions, the actual carbon contents were higher than nominal batched compositions, presumably due to carbon uptake from the graphite furnace and hot press dies. Selected area electron diffraction and neutron powder diffraction revealed the presence of carbon vacancy ordering in ZrCx for 0.6 < x < 0.75. Rietveld refinement of the neutron diffraction patterns determined that the crystal structure of the ordered phase was hexagonal, and the carbon site occupancies were higher than nominal batched carbon stoichiometry.

Al‐Cu‐Fe alloys in the solar system: Going inside a Khatyrka‐like micrometeorite (KT01) from the Nubian Desert, Sudan

AbstractA recently described micrometeorite from the Nubian desert (Sudan) contains an exotic Al‐Cu‐Fe assemblage closely resembling that observed in the Khatyrka chondrite (Suttle et al., 2019; Science Reports 9:12426). We here extend previous investigations of the geochemical, mineralogical, and petrographic characteristics of the Sudan spherule by measuring oxygen isotope ratios in the silicate components and by nano‐scale transmission electron microscopy study of a focused ion beam foil that samples the contact between Al‐Cu alloys and silicates. O‐isotope work indicates an affinity to either OC or CR chondrites, while ruling out a CO or CM precursor. When combined with petrographic evidence we conclude that a CR chondrite parentage is the most likely origin for this micrometeorite. SEM and TEM studies reveal that the Al‐Cu alloys mainly consist of Al metal, stolperite (CuAl), and khatyrkite (CuAl2) together with inclusions in stolperite of a new nanometric, still unknown Al‐Cu phase with a likely nominal Cu3Al2 stoichiometry. At the interface between the alloy assemblage and the surrounding silicate, there is a thin layer (200 nm) of almost pure MgAl2O4 spinel along with well‐defined and almost perfectly spherical metallic droplets, predominantly iron in composition. The study yields additional evidence that Al‐Cu alloys, the likely precursors to quasicrystals in Khatyrka, occur naturally. Moreover, it implies the existence of multiple pathways leading to the association in reduced form of these two elements, one highly lithophile and the other strongly chalcophile.

On Structural and Magnetic Properties of Substituted SmCo5 Materials.

SmCo5 is a well-established material in the permanent magnet industry, a sector which constantly gains market share due to increasing demand but also suffers from criticality of some raw materials. In this work we study the possibility of replacement of Sm with other, more abundant rare earth atoms like Ce-La. These raw materials are usually called "free" rare-earth minerals, appearing as a by-product during mining and processing of other raw materials. Samples with nominal stoichiometry Sm1-xMMxCo5 (x = 0.1-1.0) were prepared in bulk form with conventional metallurgy techniques and their basic structural and magnetic properties were examined. The materials retain the hexagonal CaCu5-type structure while minor fluctuations in unit cell parameters as observed with X-ray diffraction. Incorporation of Ce-La degrade intrinsic magnetic properties, Curie temperature drops from 920 K to 800 K across the series and mass magnetization from 98 Am2/kg to 60 Am2/kg; effects which trade off for the significantly reduced price. Atomistic simulations, implemented based on Density Functional Theory calculations are used in the case of the stoichiometry with x = 0.5 to calculate atomic magnetic moments and provide additional insight in the complex interactions that dominate the magnetic properties of the material.

Carbonate dimorphism, and the reinterpretation of rates of lattice and excess oxygen-driven catalytic cycles

Catalytic implications of local deviations from nominal oxide stoichiometry remain critical to consider yet challenging to elucidate in the context of bulk oxide-mediated light alkane oxidation reactions, in part due to a lack of a priori knowledge of surface active oxygen site counts. Carbonate dimorphism, i.e., differences in carbonate speciation resulting from CO2 adsorption onto unsupported nickel oxide surfaces, can be exploited toward quantifying the surface density of lattice and excess oxygens, and to further deconvolute their respective contributions toward specific steps within the ethane oxidation reaction network. Density functional theory, volumetric gas sorption, in situ titration, in situ spectroscopy, and transient kinetic data interpreted in light of quantitative estimates of surface excess oxygen density confirm the involvement of excess oxygen in partial oxidative turnovers producing ethene from ethane and O2. These collective studies cast a more nuanced interpretation of site requirements pertaining to nickel oxide-mediated alkane oxidation. Our findings reveal that excess oxygen atoms can be titrated under reaction conditions, and that these sites are (on average) more selective to ethene than lattice oxygens. Tools and methodologies employed herein connect seemingly disparate elements of bulk oxide catalysis research – the need for quantitative estimates of oxide surface non-stoichiometry on the one hand, and the propensity of unsupported oxides toward carbonate formation on the other – and provide a template for the possible broader application of quantitative analyses of probe-molecule binding characteristics toward elucidation of active site density and speciation in catalytic partial oxidation reaction systems of commercial relevance.

Intriguing Prospects of a Novel Magnetic Nanohybrid Material: Ferromagnetic FeRh Nanoparticles Grown on Nanodiamonds

A novel endeavor based on the synthesis, characterization and study of a hybrid crystalline magnetic nanostructured material composed of bimetallic iron–rhodium nanoalloys, grown on nanodiamond nanotemplates, is reported in this study. The development of this hybrid magnetic nanomaterial is grounded in the combination of wet chemistry and thermal annealing under vacuum. In order to assess, evaluate and interpret the role and special properties of the nanodiamond supporting nanotemplates on the growth and properties of the bimetallic ferromagnetic Fe–Rh nanoparticles on their surfaces, unsupported free FeRh nanoparticles of the same nominal stoichiometry as for the hybrid sample were also synthesized. The characterization and study of the prepared samples with a range of specialized experimental techniques, including X-ray diffraction, transmission and scanning transmission electron microscopy with energy dispersive X-ray analysis, magnetization and magnetic susceptibility measurements and 57Fe Mössbauer spectroscopy, reveal that thermal annealing of the hybrid sample under specific conditions (vacuum, 700 °C, 30 min) leads to the formation of a rhodium-rich FeRh alloy nanostructured phase, with an average particle size of 4 nm and good dispersion on the surfaces of the nanodiamond nanotemplates and hard ferromagnetic characteristics at room temperature (coercivity of ~500 Oe). In contrast, thermal annealing of the unsupported free nanoparticle sample under the same conditions fails to deliver ferromagnetic characteristics to the FeRh nanostructured alloy phase, which shows only paramagnetic characteristics at room temperature and spin glass ordering at low temperatures. The ferromagnetic nanohybrids are proposed to be exploited in a variety of important technological applications, such as magnetic recording, magnetic resonance imaging contrast and magnetic hyperthermia agents.

Synthesis of (Ca, Ba) co-substituted SrMoO4 hierarchical microstructures and their composition-dependent structural and optical properties

In this work, a series of Sr1-xBaxMoO4, Sr1-xCaxMoO4, and Sr1-2xCaxBaxMoO4 nanocrystal solid-solutions with well-defined morphologies have been prepared by a surfactant-free coprecipitation method at room temperature. X-ray diffraction, Rietveld refinement data, Fourier transform Raman, and Fourier transform infrared spectroscopies confirmed the formation of continuous-solid solutions over the entire composition range for Sr1-xCaxMoO4 and Sr1-xBaxMoO4. The substitution of Ca and Ba for Sr in Sr1-2xCaxBaxMoO4 leads to phase-pure powders where x ≤ 0.1. X-ray fluorescence spectroscopy confirms that the actual composition is close to the nominal stoichiometry of the samples. The molybdate powders are composed of micronic particles having diverse morphologies, including shuttle, microsphere, flower, dumbbell, and spindle. These superstructures are composed of primary particles having an average particle size of less than 60 nm. The optical band gap of Sr1-xBaxMoO4 and Sr1-xCaxMoO4 varies from 4.17 to 4.34 and 4.17 to 3.87 eV, respectively, with the chemical composition (x). The bandgap of Sr1-2xCaxBaxMoO4 is not significantly affected by variation of the nominal composition(x). The relatively small bandgap bowing parameter indicates good miscibility of the alloying constituents.

The impact of feedstock size and composition on the hydrothermal growth of (U,Th)O2

Bulk crystal growth of refractory oxides requires unique approaches, and the UxTh1-xO2 solid solution is no exception. Hydrothermal transport reactions of U0.1Th0.9O2 onto ThO2 seeds with feedstocks comprised of U0.1Th0.9O2 or mixtures of UO2 and ThO2 with a nominal composition of U0.1Th0.9O2 are investigated with µ-Raman spectroscopy and X-ray fluorescence. In each case, the trends in stoichiometry as a function of distance from the seed are analyzed and the deviations from the nominal stoichiometry discussed. When the feedstock is composed of mixed oxides, the particle surface area’s influence on the feedstock dissolution rate is the dominant factor and can produce U-rich stoichiometries as high as U0.75Th0.25O2. When composed solely of U0.1Th0.9O2, the total growth amount depends on the particle size, but the obtained stoichiometry is the product of differing solubilities. Although the U0.1Th0.9O2 feedstock produces the most homogeneous growth, the ending growth of the smallest particle UO2/ThO2 mixture yields the stoichiometry closest to U0.1Th0.9O2. How to obtain desired stoichiometries from mixtures by matching the particle size and solubilities is briefly discussed.

Reduced synthesis temperatures of SrNbO2N perovskite films for photoelectrochemical fuel production

Perovskite oxynitrides, such as SrNbO2N, have been shown to be promising materials for photoanodes in tandem photoelectrochemical cells, due to their suitable bandgap and charge transport. However, thin film synthesis and characterization of oxynitride perovskites are challenging due to high processing temperatures that are incompatible with available substrates. In this work, we report on reduced synthesis temperatures of SrNbO2N perovskite thin films on Si substrates across a range of chemical compositions. Polycrystalline thin films with perovskite crystal structure are obtained by sputtering at ambient temperature and annealing at 550–600 °C. The perovskite structure has a relatively broad range of cation composition between 50 and 60% Sr with varying O/N ratio according to Rutherford backscattering spectrometry. The maximum photocurrent density was obtained at 55 cation % of Sr, which is slightly Sr-rich compared to the nominal SrNbO2N stoichiometry. This work shows the importance of considering cation and anion composition in studying oxynitride perovskites for solar fuel applications.

Elaboration, characterization, and giant dielectric permittivity in solid state synthesized Fe half-doped LaCrO3 perovskite

LaFe0.5Cr0.5O3 (LFCO) perovskite was synthesized by conventional solid-state reaction process in air atmosphere. X-ray powder diffraction data revealed that the sample crystallizes in a Pnma orthorhombic symmetry, with a nearly same shaped grain size of 0.21–0.57 µm as shown from scanning electron microscope (SEM) images. The elemental composition of the sample with nominal stoichiometry is verified by energy-dispersive X-ray spectroscopy (EDS) results. The octahedral coordination of iron and chromium ions in the LaFe0.5Cr0.5O3 system is evidenced by the infrared spectroscopy. Impedance spectroscopy and dielectric measurements are performed in a wide frequency range at various temperatures. The higher values of ɛ′ at low frequencies are explained on the basis of the Maxwell-Wagner (MW) relaxation model arising from the inhomogeneity conduction in the grains and grain boundaries. These findings have been further confirmed by the complex impedance analysis highlighting two electrical responses attributed to grain and grain boundaries effects, respectively. Negative temperature coefficient of resistance (NTCR) effect was also proved on the material.

Zoology of spin and orbital fluctuations in ultrathin oxide films

Many metallic transition-metal oxides turn insulating when grown as films that are only a few unit-cells thick. The microscopic origins of these thickness induced metal-to-insulator transitions however remain under dispute. Here, we simulate the extreme case of a monolayer of an inconspicuous correlated metal -- the strontium vanadate SrVO$_3$ -- deposited on a SrTiO$_3$ substrate. Crucially, our system can have a termination to vacuum consisting of either a SrO or a VO$_2$ top layer. While we find that both lead to Mott insulating behavior at nominal stoichiometry, the phase diagram emerging upon doping -- chemically or through an applied gate voltage -- is qualitatively different. Indeed, our many-body calculations reveal a cornucopia of nonlocal fluctuations associated with (in)commensurate antiferromagnetic, ferromagnetic, as well as stripe and checkerboard orbital ordering instabilities. Identifying that the two geometries yield crystal-field splittings of opposite signs, we elucidate the ensuing phases through the lens of the orbital degrees of freedom. Quite generally, our work highlights that interface and surface reconstruction and the deformation or severing of coordination polyhedra in ultra-thin films drive rich properties that are radically different from the material's bulk physics.

Influence of the stoichiometry, microstructure, and metallization method on the dielectric properties of 0.94 Na0.5Bi0.5TiO3‐0.06 BaTiO3

AbstractThe morphotropic composition of the lead‐free solid solution between Na0.5Bi0.5TiO3 and BaTiO3 (0.94 Na0.5Bi0.5TiO3‐0.06 BaTiO3 or NBT‐6BT) is of particular interest for the next generation of high‐temperature capacitors but remains plagued by the diversity of dielectric properties reported in the literature. In order to explain the apparent inconsistencies among the reported dielectric properties of NBT‐6BT, we examine the influence of stoichiometry, phase separation, and metallization method. We show that the nominal stoichiometry has a crucial effect, since increasing the nominal Na/Bi ratio increases conductivity and dielectric losses (tan δ). It also increases the real part of the permittivity (ε’) and the frequency dispersion of both ε’ and tan δ, thereby altering the shape of the evolution with temperature of the dielectric properties. Moreover it increases the depolarization temperature (Td) and decreases the temperature of maximum permittivity (Tm). Phase separation also occurs during the synthesis of NBT‐6BT as Na evaporation leads to the formation of secondary Ba‐containing phases. We report that these phases can have a positive impact on the dielectric properties: a moderate volume fraction (2.5 to 3.0%) and average grain surface (0.9 to 3.0 µm2) of these secondary Ba‐containing phases increase the relative permittivity, decrease the dielectric losses, and increase the insulation resistance. We also show that the metallization method impacts the dielectric properties and therefore may contribute to the differences between various reports. The dielectric properties of NBT‐6BT samples are measured during successive heating/cooling cycles and reveal that the permittivity value is lower during the first heating when silver paste, even cured, is used. These three components contribute to explaining the diversity of the reported dielectric properties of NBT‐6BT.

Europium Addition Reduces Local Structural Disorder and Enhances Photoluminescent Yield in Perovskite CsPbBr3

AbstractCorrelative X‐ray microscopy, including synchrotron X‐ray diffraction and fluorescence, is leveraged to understand the local role of europium as a B‐site additive in CsPbBr3 perovskite crystals. Europium addition reduces microstrain in the perovskite, despite the fact that the degree of europium incorporation into the perovskite varies locally, with a maximum loading over twice the nominal stoichiometry. The presence of europium improves photoluminescence yield and bandwidth, while shifting the emission to bluer wavelengths. Finally, europium‐containing crystals have greatly improved X‐ray hardness. The findings show promise for europium as an additive in perovskite optoelectronic devices.

Inelastic background modelling applied to hard X-ray photoelectron spectroscopy of deeply buried layers: A comparison of synchrotron and lab-based (9.25 keV) measurements

Hard X-ray Photoelectron Spectroscopy (HAXPES) provides minimally destructive depth profiling into the bulk, extending the photoelectron sampling depth. Detection of deeply buried layers beyond the elastic limit is enabled through inelastic background analysis. To test the robustness of this technique, we present results on a thin (18 nm) layer of metal–organic complex buried up to 200 nm beneath organic material. Overlayers with thicknesses 25–140 nm were measured using photon energies ranging 6–10 keV at the I09 end station at Diamond Light Source, and a new fixed energy Ga Kα (9.25 keV) laboratory-based HAXPES spectrometer was also used to measure samples with overlayers up to 200 nm thick. The sampling depth was varied: at Diamond Light Source by changing the photon energy, and in the lab system by performing angle-resolved measurements. For all the different overlayers and sampling depths, inelastic background modelling consistently provided thicknesses which agreed, within reasonable error, with the ellipsometric thickness. Relative sensitivity factors were calculated, and these factors consistently provided reasonable agreement with the expected nominal stoichiometry, suggesting the calculation method can be extended to any element. These results demonstrate the potential for the characterisation of deeply buried layers using synchrotron and laboratory-based HAXPES.

Control of germanium diffusion using low quantities of co-implanted silicon isotopes

The thermal diffusion of Ge implanted into SiO2 films growth on a Si substrate has been studied by nuclear analyses and μ-Raman spectroscopy with and without the presence of co-implanted 30Si and 29Si barriers, each located from both sides of the Ge implanted distribution. Combination of Rutherford backscattering spectroscopy and Resonant nuclear reaction analysis shows that, under thermal activation at 1100°C, implanted Ge diffuses differently toward the sample surface and the SiO2/Si interface due to the occurrence of Ge outgassing effects, as well as the non-homogenous distributions of the implanted ion species and the defects they have generated inside SiO2. A maximum local atom concentration of co-implanted silicon as low as ∼1.6 at. % is found to completely block the germanium diffusion in both directions, leading to the formation of Ge nanocrystals and Si/Ge aggregates evidenced by μ-Raman spectroscopy. In addition to highlighting the role of Si excess on the Ge trapping mechanism, such a result makes the nominal silicon oxide stoichiometry and composition two crucial parameters to stabilize Ge during high temperature annealing, which explains the strong discrepancies reported for the Ge thermal diffusion coefficient in the literature.

The formation of stoichiometric uranium brannerite (UTi2O6) glass-ceramic composites from the component oxides in a one-pot synthesis

Brannerite glass-ceramic composites have been suggested as suitable wasteform materials for high-actinide content wastes, but the formation of glass-ceramic composites containing stoichiometric uranium brannerite (UTi2O6) has not been well-studied. Uranium brannerite glass-ceramic composites were synthesised at by a one-pot cold-press and sinter route from the component oxides. As a comparison, two further samples were produced using an alkoxide-nitrate route. A range of compositions with varying molar ratios of uranium and titanium oxides (from 1:2 to 1:3.20) were synthesised, with a range of different heat treatments (1200 °C for 12–48 h, and 1250 °C for 12 h). All compositions were analysed by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray near-edge spectroscopy, and found to contain UTi2O6 as the majority crystalline phase forming within a glass matrix of nominal stoichiometry Na2AlBSi6O16. In compositions with UO2:TiO2 ratios of 1:2 and 1:2.28, particles of UO2 were observed in the glass matrix, likely due to dissolution of TiO2 in the glass phase; this was prevented by the addition of excess TiO2. This work demonstrates the suitability of this system to produce highly durable wasteforms with excellent actinide waste loading, even with a simple one-pot process. Some grains of brannerite consist of a UO2 particle encapsulated in a shell of UTi2O6, suggesting that brannerite crystallises around particles of UO2 until either the UO2 is fully depleted, or the kinetic barrier becomes too large for further diffusion to occur. We propose that the formation of brannerite within glass-ceramic composites at lower temperatures than that for pure ceramic brannerite is caused by an increase in the rate of diffusion of the reactants within the glass.