Extensive Solid Solution Research Articles

Resolving phase stability in the Ti-O binary with first-principles statistical mechanics methods

The Ti-O system consists of a multitude of stable and metastable oxides that are used in wide ranging applications. In this work we investigate phase stability in the Ti-O binary from first principles. We perform a systematic search for ground state structures as a function of oxygen concentration by considering oxygen-vacancy and/or titanium-vacancy orderings over four parent crystal structures: (i) hcp Ti, (ii) $\ensuremath{\omega}$-Ti, (iii) rocksalt, and (iv) hcp oxygen containing interstitial titanium. We explore phase stability at finite temperature using cluster expansion Hamiltonians and Monte Carlo simulations. The calculations predict a high oxygen solubility in hcp Ti and the stability of suboxide phases that undergo order-disorder transitions upon heating. Vacancy ordered rocksalt phases are also predicted at low temperature that disorder to form an extended solid solution at high temperatures. Predicted stable and metastable phase diagrams are qualitatively consistent with experimental observations, however, important discrepancies are revealed between first-principles density functional theory predictions of phase stability and the current understanding of phase stability in this system.

Perovskite classification: An Excel spreadsheet to determine and depict end-member proportions for the perovskite- and vapnikite-subgroups of the perovskite supergroup

Perovskite mineral oxides commonly exhibit extensive solid-solution, and are therefore classified on the basis of the proportions of their ideal end-members. A uniform sequence of calculation of the end-members is required if comparisons are to be made between different sets of analytical data. A Microsoft Excel spreadsheet has been programmed to assist with the classification and depiction of the minerals of the perovskite- and vapnikite-subgroups following the 2017 nomenclature of the perovskite supergroup recommended by the International Mineralogical Association (IMA). Compositional data for up to 36 elements are input into the spreadsheet as oxides in weight percent. For each analysis, the output includes the formula, the normalized proportions of 15 end-members, and the percentage of cations which cannot be assigned to those end-members. The data are automatically plotted onto the ternary and quaternary diagrams recommended by the IMA for depiction of perovskite compositions. Up to 200 analyses can be entered into the spreadsheet, which is accompanied by data calculated for 140 perovskite compositions compiled from the literature.

Structural Transformation of LiFePO4 during Ultrafast Delithiation.

The prolific lithium battery electrode material lithium iron phosphate (LiFePO4) stores and releases lithium ions by undergoing a crystallographic phase change. Nevertheless, it performs unexpectedly well at high rate and exhibits good cycling stability. We investigate here the ultrafast charging reaction to resolve the underlying mechanism while avoiding the limitations of prevailing electrochemical methods by using a gaseous oxidant to deintercalate lithium from the LiFePO4 structure. Oxidizing LiFePO4 with nitrogen dioxide gas reveals structural changes through in situ synchrotron X-ray diffraction and electronic changes through in situ UV/vis reflectance spectroscopy. This study clearly shows that ultrahigh rates reaching 100% state of charge in 10 s does not lead to a particle-wide union of the olivine and heterosite structures. An extensive solid solution phase is therefore not a prerequisite for ultrafast charge/discharge.

Minerals with Brackebuschite-Like Structures: A Novel Solid Solution System Involving Cr6+ and V5+

A novel complex continuous system of solid solutions involving vauquelinite Pb2Cu(CrO4)(PO4)(OH), bushmakinite Pb2Al(VO4)(PO4)(OH), ferribushmakinite Pb2Fe3+(VO4)(PO4)(OH), and a phase with the endmember formula Pb2Cu(VO4)(PO4)(H2O) or Pb2Cu(VO4)(РО3ОН)(ОН) is studied based on samples from the oxidation zone of the Berezovskoe, Trebiat, and Pervomaisko-Zverevsky deposits in the Urals, Russia. This is the first natural system in which chromate and vanadate anions show a wide range of substitutions and the most extensive solid solution system involving (CrO4)2– found in nature. The major couple substitution is Cr6+ + Cu2+ ↔ V5+ + M3+, where M = Fe, Al. The correlation coefficients calculated from 125 point analyses are: 0.96 between V and (Fe + Al), 0.96 between Cr and (Cu + Zn),–0.96 between V and (Cu + Zn),–0.97 between Cr and (Fe + Al), and–0.97 between (Fe + Al) and (Cu + Zn). The substitutions V5+ ↔ Cr6+ (correlation coefficient–0.98) and to a lesser extent P5+ ↔ As5+ (correlation coefficient–0.86) occur at two types of tetrahedral sites, whereas the metal–nonmetal/metalloid substitutions, i.e., V or Cr for P or As, are minor. The substitution Fe3+ ↔ Al3+ is also negligible in this solid solution system.

Bohseite, ideally Ca4Be4Si9O24(OH4, from the Piława Górna quarry, the Góry Sowie Block, SW Poland

AbstractBohseite is an orthorhombic calcium beryllium aluminosilicate with variable Al content and an endmember formula Ca4Be4Si9O24(OH4), that was discovered in the Piława Górna quarry in the eastern part of the Góry Sowie Block, ∼50 km southwest of Wrocław, SW Poland. It occurs in a zoned anatectic pegmatite dyke in close association with microcline, Cs-rich beryl, phenakite, helvite, 'lepidolite', probably bertrandite and unidentified Be-containing mica as alteration products after a primary Be mineral, probably beryl. Bohseite forms fan-like or parallel aggregates (up to 0.7 cm) of white, platy crystals (up to 2 mm long) with characteristic striations. It is white with a white streak, is translucent and has a vitreous lustre; it does not fluoresce under ultraviolet light. The cleavage is perfect on {001} and fair on {010}, and neither parting nor twinning was observed. Bohseite is brittle with a splintery fracture and Mohs hardness is 5–6. The calculated density is 2.719 g cm–3. The indices of refraction are α= 1.579, β = 1.580,γ = 1.597, all ±0.002; 2Vobs = 24(3)°, 2Vcalc = 27°; the optic orientation is as follows: X ^a= 16.1°, Y ^b= 16.1°, Z //cBohseite shows orthorhombic diffraction symmetry, space groupCmcm,a= 23.204(6),b= 4.9442(9),c= 19.418(6) Å,V= 2227.7(4) Å3,Z= 4. The crystal structure was refined to anR1value of 2.17% based on single-crystal data, and the chemical composition was determined by electron-microprobe analysis. Bohseite is isostructural with bavenite. Bohseite was originally approved with an end-member composition of Ca4Be3AlSi9O25(OH)3, but subsequent discovery of compositions with Be > 3.0 apfu led to redefinition of its end-member composition, holotype sample and locality, as reported here. There is extensive solid solution in bavenite–bohseite according to the schemeO(2)OH–+T(4)Si4++T(3)Be2+↔O(2)O2–+T(4)Al3++T(3)Si4+, and a general formula for the bavenite–bohseite minerals may be written as Ca4BexSi9Al4–xO28–x(OH)x, where x ranges from 2–4 apfu: Ca4Be2Si9Al2O26(OH)2(bavenite) to Ca4Be4Si9O24(OH)4(bohseite).

Isothermal Section of the Al-Mn-Dy System at 500 °C

Phase relationships in the Al-Mn-Dy ternary system at 500 °C have been investigated by X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, and electron probe microanalysis. From the experimental results it was concluded that the isothermal section consists of 16 single-phase regions, 26 two-phase regions and 12 three-phase regions. Two extensive solid solutions, (AlxMn1−x)12Dy and (Al1−xMnx)2Dy, were observed. The solid solution (AlxMn1−x)12Dy forms by Al replacing Mn in Mn12Dy, while the continuous solid solution (Al1−xMnx)2Dy forms by Mn and Al mutually substituting in Al2Dy and Mn2Dy, respectively. The maximum solid solubility of Al in Mn12Dy is 79.3 at.%.

Structural and Microstructural Properties of Si-C and Si-C-B Powders Obtained by High-Energy Ball Milling

This work evaluated on the structural modification during high-energy ball milling of the Si-50C, Si-42.9C-19.1B e Si-33.3C-44.4B (at.-%) powder mixtures from elemental powders. Electron images revealed on occurrence of continuous fracture mechanisms in brittle particles during their processing, which presented rounded particles lower than 10 μm. X-ray diffraction results of Si-50C powders indicated that the intensity of Si peaks was slightly reduced after milling for 17 h, which were moved to the direction of larger diffraction angles after 7 h of milling, suggesting that carbon atoms were dissolved into the Si lattice in order to form an extended solid solution. Following, these values were increased due to the discrete exothermic formation of the SiC compound. In Si-C-B powder mixtures, the SiC and B4C compounds were formed after milling for 7 h.

On the P–T– $$fO_{2}$$ f O 2 stability of Fe4O5, Fe5O6 and Fe4O5-rich solid solutions

The high-pressure phases Fe4O5 and Fe5O6 have recently been added to the list of known iron oxides. As mixed-valence phases, it has been suggested that they could form in the Earth’s mantle once the dominant minerals become saturated in ferric iron. The possibility that Fe4O5 could exist in the mantle is also supported by the fact that it forms extensive solid solutions with both Mg2+ and Cr3+. In this study, we present the results of high-pressure and high-temperature multi-anvil experiments performed between 5 and 24 GPa at 1000–1400 °C aimed at constraining the stability field of the Fe4O5 phase. We combine these results with published phase equilibria, equation of state and Fe–Mg partitioning data to estimate the thermodynamic properties of Fe4O5, Fe5O6 and the (Mg,Fe)2Fe2O5 solid solution. Using our thermodynamic model, the oxygen fugacity at which the high-pressure iron oxides become stable is calculated and the redox stability of (Mg,Fe)2Fe2O5 in an assemblage of olivine and pyroxene is calculated as a function of the bulk Fe/(Fe + Mg) ratio. Fe4O5 and (Mg,Fe)2Fe2O5 are stable at oxygen fugacities higher than the diamond stability field and are, therefore, unlikely to be found as inclusions in diamonds. The stability field of Fe5O6, on the other hand, extends to oxygen fugacities compatible with diamond formation. Using the Mg–Fe solid solution model, we show that Fe4O5-structured phases would be restricted to aluminium-poor environments in the mantle such as dunites or silica–iron oxide-rich sediments transported into the mantle via subduction.

Phase Equilibrium Studies of CaO-SiO2-MgO-Al2O3 System with Binary Basicity of 1.5 Related to Blast Furnace Slag

Slags play an important role in blast furnace operation, and their compositions are based on the CaO-SiO2-MgO-Al2O3 quaternary system in many steel companies. The binary basicity (CaO/SiO2 weight ratio) of blast furnace slags, especially primary slag and bosh slag, can be as high as 1.5 or higher. Phase equilibria and liquidus temperatures in the CaO-SiO2-MgO-Al2O3 system with binary basicity of 1.50 are experimentally determined for temperatures in the range 1723 K to 1823 K (1450 °C to 1550 °C). High temperature equilibration, quenching, and electron probe X-ray microanalysis techniques have been used in the present study. The isotherms are obtained in the primary phase fields of Ca2SiO4, melilite, spinel, periclase, and merwinite related to blast furnace slags. Effects of Al2O3, MgO, and binary basicity on liquidus temperatures have been discussed. In addition, extensive solid solutions have been measured for different primary phases and will be used for development and optimization of the thermodynamic database.

Phase Equilibria in the System “FeO”–CaO–SiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub>–MgO with CaO/SiO<sub>2</sub> 1.3

A series of FeO-containing slags are present in iron blast furnace. Phase equilibria play an important role in optimum operation of blast furnace which involves complex chemical reactions. Phase equilibria studies have been carried out in the system FeO-CaO-SiO-AlO-MgO in equilibrium with metallic iron. The technique used includes high temperature equilibration followed by quenching and electron probe X-ray microanalysis. Pseudo-ternary sections of the phase diagrams are presented in the form of (CaO+SiO)-AlO-MgO at fixed CaO/SiO ratio of 1.3 and FeO concentrations of 5 and 10 wt%. This is the first systematic study in the system FeO-CaO-SiO-AlO-MgO important to the blast furnace operations. It was found that melilite, Ca2SiO4, merwinite, spinel and (Mg,Fe2+)O are the primary phase fields in the composition range investigated. Liquidus temperatures increase in the melilite and spinel primary phase fields and decrease in the merwinite and CaSiO primary phase fields with increasing AlO concentration. The liquidus temperature is not sensitive with AlO in the spinel primary phase field. Effects of MgO and FeO on liquidus temperature are also discussed. Extensive solid solutions can be formed in this system that have significant influence on the liquidus temperatures and the data will be used for optimisation of the thermodynamic models.

Coupled Experimental and Thermodynamic Optimization of the Na2O–FeO–Fe2O3–Al2O3 System: Part 1. Phase Diagram Experiments

As part of the complete thermodynamic modeling of the Na2O–FeO–Fe2O3–Al2O3 system, the Na2O–FeO–Fe2O3–Al2O3 phase diagrams in air (1583 and 1698 K) and at Fe saturation (1573 and 1673 K) were investigated using the quenching method followed by Electron Probe Micro‐Analyzer (EPMA) and X‐ray Diffraction (XRD) phase analysis. General features of the phase diagrams in this system were well revealed for the first time. A complete meta‐oxide solid solution between NaAlO2 and NaFeO2 was observed. An extensive solid solution of Na2(Al,Fe)12O19 Na‐βˮ‐alumina was found and the existence of a miscibility gap in this solution was confirmed. Several compatibility triangles of three‐phase assemblages were also identified in air and at Fe saturation.

The Nanocrystalline SnO2–TiO2 System‒Part II: Surface Energies and Thermodynamic Stability

The thermodynamic stability of nanocrystalline SnO2–TiO2 solid solutions was studied experimentally. Microcalorimetry of water adsorption revealed a systematic decrease in the surface energy with increasing Ti4+ content in the SnO2‐rich compositions, consistent with previous reports of Ti4+ segregation on the surface. The surface energy change was accompanied by an increase in the magnitude of the heat of water adsorption, also indicating a modification of the SnO2 surface by Ti4+. Supporting the water adsorption data, calculations using high‐temperature oxide melt solution calorimetry data also suggest a decrease in the interface energies. A thermodynamic analysis showed that the observed surface energy decrease is responsible for an increase in the stability of solid solutions in the nanophase regime. Although a miscibility gap is expected in this system from bulk phase diagrams, the surface energy contribution modifies the bulk trend and promotes extensive solid solutions when the surface area is above a critical value dependent on the surface energy and the bulk enthalpy of mixing.

Synthesis and mineralogical characteristics of hydroxylapatite-hydroxylpyromorphite solid solution series Ca5(PO4)3OH–Pb5(PO4)3OH

Lead is a widespread environmental contaminant toxic to living organisms. Soils and wastes contaminated with Pb are found in both rural and urban settings. Uptake of Pb from waste, soil or water by phosphate compounds, particularly hydroxylapatite, has been proved as effective remediation strategy (Xu and Schwartz, 1994). The technology arises from the low solubility of lead apatites and from their rapid precipitation reactions. The structure of apatites can be described by the general formula A 5 (BO 4 ) 3 C, where A: Ca, Pb, Sr, Ba; B: P, As, V; C: Cl, OH, F, Br, I. Apatites are very tolerant to structural distortion resulting from chemical substitution in cationic and anionic positions and consequently they are remarkably diverse in composition. The hydroxylapatite’s structure also allows for extended substitutions of cations and anions. It is hypothesized here that, thanks to the potential for extensive solid solutions in the system, the lead apatites precipitating in the environment are not pure end members but rather Pb-Ca solid solutions. A complete solid solution between hydroxylapatite (HAP) and hydroxylpyromorphite (HPY) was determined before (Bigi et al., 1991; Hadrich et al., 2001). The results, however, are still fragmentary and partly inconsistent. The objective of the project is systematic characterization (crystal structure as well as infrared and Raman vibrtational properties) of synthetic analogs of the minerals from HAP – HPY solid solution series. This will allow to clarify the controversies. Well characterized products of the synthesis will be used in future in thermodynamic study of solubility changes with substitution, which was never determined before. It is assumed that the properties vary in systematic way with Pb substitution for Ca. An effective wet method of synthesis of Ca-Pb apatites was developed. A crystalline, homogeneous precipitates with stoichiometric composition were produced. Six phases of HAP-HPY solid solution series were prepared by dropwise mixing of a solution containing calcium and/or lead ions and a phosphate solution at room temperature. During the synthesis pH of 8,5 was maintained using NH 4 OH. Precipitates were washed, air dried and characterized by scanning electron microscopy (SEM/EDS), powder X-ray diffraction, infrared spectroscopy (FTIR) and Raman spectroscopy. All synthetic products obtained in the experiments form hexagonal needles less than 0.1 µm long. Elemental composition is consistent with theoretical stoichiometry of the phases. X-ray diffraction patterns reveal a shift toward lower angles 2θ for phases with higher lead contents. This indicates an enlargement of the lattice constants. The variation of parameters, however, is not linear (does not follow the Vegard’s law). Particularly the cell parameter c changes more for phases reach in lead. These results are in agreement with those reported previously (Bigi et al., 1991; Hadrich et al., 2001). A shift of band position is also observed in both FTIR and Raman spectra. All the bands shift towards lower wavenumber with increasing Pb content. In most cases the shift is not linear exhibiting two trends similar to lattice parameters. This may indicate that the vibrational properties of the phases in the series depend stronger on the bond length than on the atomic mass of substituting elements. This work was supported by AGH-UST statutory grant No. 11.11.140.319.

Thermodynamic mixing properties of the UO2–HfO2 solid solution: Density functional theory and Monte Carlo simulations

HfO2 is a neutron absorber and has been mechanically mixed with UO2 in nuclear fuel in order to control the core power distribution. During nuclear fission, the temperature at the center of the fuel pellet can reach above 1300K, where hafnium may substitute uranium and form the binary solid solution of UO2–HfO2. UO2 adopts the cubic fluorite structure, but HfO2 can occur in monoclinic, tetragonal, and cubic structures. The distribution of Hf and U ions in the UO2–HfO2 binary and its atomic structure influence the thermal conductivity and melting point of the fuel. However, experimental data on the UO2–HfO2 binary are limited. Therefore, the enthalpies of mixing of the UO2–HfO2 binary with three different structures were calculated in this study using density functional theory and subsequent Monte Carlo simulations. The free energy of mixing was obtained from thermodynamic integration of the enthalpy of mixing over temperature. From the ΔG of mixing, a phase diagram of the binary was obtained. The calculated UO2–HfO2 binary forms extensive solid solution across the entire compositional range, but there are a variety of possible exsolution phenomena associated with the different HfO2 polymorphs. As the structure of the HfO2 end member adopts lower symmetry and becomes less similar to cubic UO2, the miscibility gap of the phase diagram expands, accompanied by an increase in cell volume by 7–10% as the structure transforms from cubic to monoclinic. Close to the UO2 end member, which is relevant to the nuclear fuel, the isometric uranium-rich solid solutions exsolve as the fuel cools, and there is a tendency to form the monoclinic hafnium-rich phase in the matrix of the isometric, uranium-rich solid solution phase.

Phosphates having the NaZr2(PO4)3 structure and containing titanium (or zirconium) and elements in oxidation degree 2+ (calcium or zinc)

Complex phosphates Ca0.5 + x Zn x E2 − x (PO4)3 (E = Ti, Zr) having NaZr2(PO4)3 (NZP) structure have been prepared and characterized by X-ray diffraction, electron probe microanalysis, IR spectroscopy, and differential thermal analysis (DTA). Their phase formation has been studied by X-ray powder diffraction and DTA. The concentration and temperature fields of existence of these NZP phases have been determined: substitution solid solutions exist in the range of compositions where 0 ≤ x ≤ 0.5. The Ca0.7Zn0.2Ti1.8(PO4)3 crystal structure has been refined by the Rietveld method (space group \(R\bar 3\), a = 8.3636(4) A, c = 21.9831(8) A, V = 1331.7(1) A3, Z = 6). The framework in the NZP structure is built of octahedra, which are populated by titanium and zinc atoms, and PO4 tetrahedra. Calcium atoms occupy extraframework positions. Extensive solid solution formation due to the accommodation of cations(2+) in the interstices within the NZP framework (M) and in the framework-forming octahedra (M′) makes it possible to design a plurality of new M0.5 + x M′ x E2 − x (PO4)3 phosphates with tailored structures.

Metastability in the MgAl2O4–Al2O3 System

Aluminum oxide must take a spinel form (γ‐Al2O3) at increased temperatures in order for extensive solid solution to form between MgAl2O4 and α‐Al2O3. The solvus line between MgAl2O4 and Al2O3 has been defined at 79.6 wt% Al2O3 at 1500°C, 83.0 wt% Al2O3 at 1600°C, and 86.5 wt% Al2O3 at 1700°C. A metastable region has been defined at temperatures up to 1700°C which could have significant implications for material processing and properties. Additionally, initial processing could have major implications on final chemistry.

Chemically Strengthened Low Crystallinity Black Glass‐Ceramics with High Liquidus Viscosities

Strong, black materials are needed for electronic device backs and appliance facings. While glass‐ceramics have good strength and toughness, their liquidus viscosity is too low to enable economical forming of these devices by the fusion or slot draw methods. Thus, we invented a new class of low crystallinity glass‐ceramics with 10–20 nm crystallites in the Fe2O3‐TiO2‐MgO system. These materials were formed into transparent glasses and then heat treated to make black opaque glass‐ceramics containing magnetite, pseudobrookite, and/or ε‐Fe2O3. The ε‐Fe2O3 phase exhibited extensive solid solution (ss) between Fe2O3 and MgTiO3. The blackness and opacity of the ε‐Fe2O3 glass‐ceramics peaked at a ceram temperature of 750°C where the Fe2+ in the crystallites was maximized, resulting in peak Fe2+‐Ti4+ charge transfer absorption. The liquidus viscosity was increased to more than 100 kPa*s by optimizing the base glass composition and minimizing the amount of crystallinity, thereby enabling fusion formability. These fusion formable glass‐ceramics had strengths exceeding the best commercially available glasses after ion exchange. This work provides a new class of low crystallinity fusion formable glass‐ceramics with high strength.

Sodium Distribution and Reaction Mechanisms of a Na3V2O2(PO4)2F Electrode during Use in a Sodium-Ion Battery

Ambient temperature sodium-ion batteries are emerging as an exciting alternative to commercially dominant lithium-ion batteries for larger scale stationary applications. In order to realize such a sodium-ion battery, electrodes need to be developed, understood, and improved. Here, Na3V2O2(PO4)2F is investigated from the perspective of sodium. Reaction mechanisms for this cathode during battery function include the following: a region comprising at least three phases with subtly varying sodium compositions that transform via two two-phase reaction mechanisms, which appears at the lower potential plateau-like region during both charge and discharge; an extended solid solution region for majority of the cycling process, including most of the higher potential plateau; and a second two-phase region near the highest charge state during charge and between the first and second plateau-like regions during discharge. Notably, the distinct asymmetry in the reaction mechanism, lattice, and volume evolution on charge relative to discharge manifests an interesting question: Is such an asymmetry beneficial for this cathode? These reaction mechanisms are inherently related to sodium evolution, which shows complex behavior between the two sodium crystallographic sites in this compound that in turn mediate the lattice and reaction evolution. Thus, this work relates atomic-level sodium perturbations directly with electrochemical cycling.

Dense Si(x)Ge(1-x) (0 < x < 1) materials landscape using extreme conditions and precession electron diffraction.

High-pressure and -temperature experiments on Ge and Si mixtures to 17 GPa and 1500 K allow us to obtain extended Ge-Si solid solutions with cubic (Ia3) and tetragonal (P4(3)2(1)2) crystal symmetries at ambient pressure. The cubic modification can be obtained with up to 77 atom % Ge and the tetragonal modification for Ge concentrations above that. Together with Hume-Rothery criteria, melting point convergence is employed here as a favored attribute for solid solution formation. These compositionally tunable alloys are of growing interest for advanced transport and optoelectronic applications. Furthermore, the work illustrates the significance of employing precession electron diffraction for mapping new materials landscapes resulting from tailored high-pressure and -temperature syntheses.

Interaction of lanthanum with boron and carbon: phase diagram and structural chemistry

The isothermal section of the La–B–C phase diagram at 1,270 K has been investigated by means of X-ray, neutron powder diffraction, microstructure and EPMA analyses. Eight ternary compounds were found, and for six of them, the crystal structures have been established. The phase with the structure type of La5B2C6 has a broad homogeneity range described by the formula La5(BC) x (5.6 ≤ x ≤ 8.8). The lanthanum sesquicarbide La2C3 exhibits an extended solid solution in the ternary domain La2C3−x B x (x = 0.4). The boron substitution of carbon leads to the decrease of the superconducting temperature from 13.4 K for La2C3 to 10.0 K for La2C2.8B0.2 and from 5.6 K for La2C2.7 to 4.1 K for La2C2.6B0.4. The compositions of two new compounds ~La4B3C12 and ~La4B5C18 were found via WDX analysis.