Photo-assisted selective catalytic reduction (photo-SCR) has been considered as a promising strategy for NOx removal in recent decades. The purpose of the present work was to test the effectiveness of La1–xPrxCoO3, supported on the surface of natural palygorskite (Pal) by a facile sol-gel method, as a photo-SCR for the removal of NOx from wastewaters. The structure, acidity, and the redox property of the prepared La1–xPrxCoO3/Pal nanocomposite were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Visible diffuse reflectance spectroscopy (UV-Vis DRS), and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) calculations were employed to determine the valence bands. The La1–xPrxCoO3/Pal catalysts were then tested for SCR removal of NOx with the assistance of photo-irradiation. The photo-SCR results revealed that the NOx conversion and the N2-selectivity were greatly improved by this method and reached >95% when carried out at the relatively low temperature of 200°C and with the Pr doping at x = 0.5. The improvements were attributed to the co-precipitation of a PrCoO3 phase as in a solid solution forming a coherent heterojunction of PrCoO3/La0.5Pr0.5CoO3 on the Pal surface.

Powder-type semiconductor photocatalysts are widely applicable but their defects (e.g. easy agglomeration during preparation and recyclability in the suspension system) limit their practical application. In the current study, perovskite oxide photocatalytic material was loaded onto a muscovite substrate to overcome the problems of low stability, easy agglomeration, and difficult recovery. A photocatalytically active LaNi0.95Fe0.05O3/muscovite composite material was synthesized by a sol-gel impregnation method. Phase composition, morphology, and interfacial interaction of the composites, denoted as LNFBY-x (x: mass ratio of LNF to muscovite), were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and other analytical methods. According to the results, the particle size of LNF nanoparticles was regulated effectively by compounding with muscovite, and the agglomeration of LNF decreased. LNF nanoparticles were distributed evenly and attached in dense fashion to the surface of muscovite, thereby increasing the contact area with the reaction medium. The nanoparticles were connected to the silicon-oxygen tetrahedral sheet of the muscovite via Si–O–La, Si–O–Ni, and Si–O–Fe bonds, which increased the bonding strength between the composite components and expedited the transfer of photogenerated charge. More highly active oxygen species were produced, and a growing number of chemically active moieties (٠O2- and ٠OH) was generated in the photocatalytic reaction. LNFBY-1.00 demonstrated the best photocatalytic activity. A degradation rate of methyl orange of 99.03% was achieved after visible-light irradiation for 120 min, which decreased to 75.75% after five repeated uses, thereby indicating high stability and recycling ability. The photocatalytic LaNi0.95Fe0.05O3/muscovite composite material exhibited potential for application in environmental remediation practices.

In the present work, LaNi0.5Ti0.5O3, LaNi0.5Ti0.45Co0.05O3, and LaNi0.45Co0.05Ti0.5O3 perovskites were synthesized using the modified Pechini method. After reduction, the studied perovskites changed crystal structure from the perovskite crystal structure to a cubic symmetry, with space group $Pm\bar{3}m$. The reduction partially decomposed the samples to Ni0 (Co free perovskite), Ni0–Co0, La2O3, La2TiO5, and non-stoichiometric La2NiO4, depending on H2 content of the reductive gases. The degree of reduction of nickel from LaNi0.5Ti0.5O3 reduced with 1.8% H2/Ar and 10% H2/Ar was equal to 36.5% and 95.3%, respectively, while that from LaNi0.5Ti0.45Co0.05O3 or LaNi0.45Co0.05Ti0.5O3, including cobalt, reduced with 10% H2/Ar, was equal to 71.9% and 93.9%, respectively. LaNi0.5Ti0.45Co0.05O3 showed Ni3+ and Co3+ amounts higher than the other perovskites. By increasing H2 content in the reductive mixture from 1.8% to 10%, sintering of metallic nickel was not observed. Moreover, Ni0 displayed weaker metal–support interaction than that observed for Co0, where the support was composed of La containing oxides. LaNi0.5Ti0.5O3 perovskite was used as a catalyst for steam reforming of methane. Syngas production was attributed to the number of Ni sites determined using Rietveld Refinement of X-ray diffraction pattern of this catalyst after the reaction.

This work is the first in situ U–Pb geochronological study of perovskite and calcic garnet (andradite) from the Guli complex in the Maimecha–Kotuy alkaline province (Polar Siberia, Russia). The U–Pb isotopic compositions of perovskite from contact zones of the two carbonatite stocks (Southern and Northern) and from jacupirangite separating the stocks were determined by laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICPMS) and isotope-dilution thermal-ionisation mass-spectrometry (ID-TIMS). The LA-ICPMS and ID-TIMS data for perovskite from the Northern carbonatite stock are in good agreement, yielding 206Pb/238U ages of 250.4 ± 1.1 Ma and 249 ± 2 Ma, respectively. These ages are also within the analytical uncertainty from the ID-TIMS results for perovskite from jacupirangites (250 ± 1 Ma). The LA-ICPMS results for perovskite from the Southern carbonatite stock indicate its somewhat older age (255.3 ± 2.4 Ma), implying the possibility of small-volume mantle magmatism predating the eruption of the Siberian flood basalts at ca. 252–251 Ma. This interpretation is supported by reports of pre-flood magmatism elsewhere in eastern Siberia. Andradite crystals from the contact between the Southern stock and metasomatised melilitolite were analysed by ID-TIMS. These measurements are inconclusive (247 ± 6 Ma) and could not be used to constrain further the timing of carbonatitic magmatism in the southern part of the complex. The present contribution also presents a refined methodology for LA-ICPMS geochronological studies of perovskite with elevated levels of common lead, and addresses some of the problems with previously proposed calibration standards.

In the present work, LaNi0.5Ti0.45Co0.05O3, LaNi0.45Co0.05Ti0.5O3, and LaNi0.5Ti0.5O3 perovskites were synthesized by the modified Pechini method. These materials were characterized using X-ray fluorescence, scanning electron microscopy, and powder X-ray diffraction coupled to the Rietveld method. The crystal structure of these materials is orthorhombic, with space group Pbnm (No 62). The unit-cell parameters are a = 5.535(5) Å, b = 5.527(3) Å, c = 7.819(7) Å, V = 239.2(3) Å3, for the LaNi0.5Ti0.45Co0.05O3, a = 5.538(6) Å, b = 5.528(4) Å, c = 7.825(10) Å, V = 239.5(4) Å3, for the LaNi0.45Co0.05Ti0.5O3, and a = 5.540(2) Å, b = 5.5334(15) Å, c = 7.834(3) Å, V = 240.2(1) Å3, for the LaNi0.5Ti0.5O3.

Polycrystalline Ca0.925Ce0.075Mn0.9Fe0.1O3 were prepared by sol-gel reaction at 1073 K. The compound was analyzed by a powder X-ray diffraction technique and found to be in single phase. The unit-cell parameters and atomic positions were refined using General Structure Analysis to an orthorhombic structure with space group Pnma (#62) a = 5.281 90 (33) Å, b = 7.4968 (45) Å, and c = 5.302 90 (32) Å.

Stable perovskite and metastable post-perovskite NaCoF3 were deformed in pure-shear geometry in a deformation-DIA press with radiographic monitoring of the sample strain. In isothermal experiments where there was no transformation, post-perovskite was found to be 5 times weaker than perovskite. In temperature-ramping experiments where post-perovskite transformed to perovskite during the deformation experiment the initial post-perovskite sample was 5–10 times weaker than perovskite under comparable conditions and their strengths converged during the transformation, being equal on completion of the transformation. These results confirm recent findings which show that postperovskite is weaker than perovskite, regardless of the prior history of the sample.

Perovskite compositions are used to investigate the relationship between the minor components (i.e. LREE, Fe3+ and Nb) and the oxygen fugacity (fo2) of perovskite in four different kimberlite lithofacies from the Dutoitspan pipe, Kimberley, South Africa, which range from diamondiferous to barren. The perovskite textures and chemical variations provide insight into magmatic and eruptive processes. Some crystals display cores with rims separated by a sharp boundary. The cores contain larger Na and LREE contents relative to the rims, which show a large increase in Fe3+ and Al. The mid-grade and barren kimberlites have bi-modal cores, reflected in the mineral chemistry, signifying multiple batches of magma and magma mixing. The fo2 of the magma is determined by an Fe-Nb oxygen barometer. The most diamondiferous kimberlite has the greatest Fe3+ content and highest fo2 (NNO –3.6 to –1.1). The kimberlite containing large diamonds has the smallest Fe3+ content and lowest fo2 (NNO –5.2 to –3.0). The barren and mid-grade kimberlites display a wide range of fo2,(NNO –5.3 to –1.5) as a result of perovskites forming in different melts and subsequently mixing together. Chemical and petrological evidence suggests that the volatile content, degassing, decompression and rate of crystallization can influence the rate at which the magma is erupted. One possibility is that the most oxidized magma, containing the highest volatile content, is therefore erupted much more rapidly, preserving diamond as a consequence.

Most countries intend to dispose of their high-level radioactive wastes by converting them into a solidified wasteform which is to be buried within the earth. SYNROC is a titanate ceramic wasteform which has been designed for this purpose on the basis of geochemical principles. It comprises essentially rutile TiO2, ‘hollandite’ Ba(Al,Ti)Ti6O16, zirconolite CaZrTi2O7, and perovskite CaTiO3. The latter three phases have the capacity to accept the great majority of radioactive elements occurring in high-level wastes into their crystal lattice sites. These minerals (or their close relatives) also occur in nature, where they have demonstrated their capacity to survive for many millions of years in a wide range of geological environments. The properties of SYNROC and the crystal chemistry of its constituent minerals are reviewed in some detail and current formulations of SYNROC are summarized. A notable property of SYNROC it its extremely high resistance to leaching by groundwaters, particularly above 100°C. In addition, it can be shown that the capacity of SYNROC minerals to immobilize high-level waste elements is not markedly impaired by high levels of radiation damage. Current investigations are focused on developing a satisfactory production technology for SYNROC and progress towards this objective is described. The high leach resistance of SYNROC at elevated temperatures increases the range of geological environments in which the waste may be finally interred; in particular, SYNROC is well adapted for disposal in deep drill-holes, both in continental and marine environments. The fact that SYNROC is comprised of minerals which have demonstrated long-term geological stability is significant in establishing public confidence in the ability of the nuclear industry to immobilize high-level wastes for the very long periods required.

Selected-area electron diffraction patterns for the [110] zone of MgSiO3 perovskite are consistent with the orthorhombic unit cell obtained by X-ray diffraction (a = 4.775, b = 4.929, c = 6.897 Å). Various areas of a crystal fragment show diffuse streaking along c*, and well-developed satellite reflections that give a 3-fold repeat along [10]*. Another fragment shows doubled cell dimensions when viewed down [30]. The variable occurrence of the satellite reflectioncs and diffuse streaking indicate subtle variations in ordering, chemistry, or both. Images obtained by high-resolution transmission electron microscopy contain perfectly ordered regions, out-of-phase boundaries, and intergrowths of the two orthorhombic forms of perovskite.

Water plays an important role in most processes within the Earth's mantle, e.g. transport phenomena, differentiation and seismic properties. This paper reviews the various aspects of water in the mantle, with a special emphasis on the water content in nominally anhydrous minerals, especially lower-mantle minerals. The saturation of the upper mantle with respect to water is calculated as a function of pressure, based on available water-solubility data obtained for upper-mantle minerals. The result indicates that the upper mantle is saturated at pressures between 2 and 4 GPa for bulk water contents of 250 to 700 ppm wt., as retrieved from measurements on mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs). Whereas up to 4000 ppm wt. of H2O could be dissolved in the upper mantle at pressures corresponding to 410 km depth, such a value is less than the 1.5–2.5 wt.% solubility stored in the hydrous phases of the transition zone. Water solubility in mantle perovskite is still controversial, because of the difficulty of synthesizing samples free of impurities. Reported data indicate that water solubility in perovskite decreases with increasing temperature and Al content. Water partitions preferentially into ferropericlase rather than into perovskite, and its water solubility increases with the incorporation of trivalent cations.

We present experimental data for the Pm3m-I4/mcm phase transitions in the perovskite crystals KMn1-xCaxF3 and SrTiO3. Comparison of calorimetric data (latent heat and specific heat) with order parameter data (measured with X-ray rocking methods) indicates that these transitions follow mean-field behaviour, and may be described using Landau potentials where the free energy expansion includes terms up to Q6. This potential is characteristic of transitions close to the tricritical point. Comparison of the behaviour of SrTiO3 and KMnF3 indicates that KMnF3 is closer to the tricritical point; a small amount of substitution of Ca for Mn causes the transition to cross the tricritical point from first order to second order behaviour.

In hypabyssal and crater-facies kimberlites of the Lac de Gras kimberlite field, perovskite occurs as reaction-induced rims on earlier-crystallized Ti-bearing minerals (magnesian ilmenite and priderite), inclusions in atoll spinels and discrete crystals in a serpentine-calcite mesostasis. The mineral is associated with spinels, apatite, monticellite, phlogopite, baryte, Fe-Ni sulphides, ilmenite, diopside and zircon. Uncommon accessory phases found in an assemblage with perovskite include titanite, monazite- (Ce), witherite, strontium-apatite, khibinskite, djerfisherite, wollastonite, pectolite, suolunite, hydroxyapophyllite and bultfonteinite. Three types of perovskite can be distinguished on the basis of composition: (I) REE-Nb-Al-poor perovskite with relatively high Sr and K contents (up to 2.2 and 0.6 wt.% oxides, respectively) occurring as mantles on priderite and inclusions in atoll spinels; (II) perovskite with elevated Al, Fe, Nb and LREE (up to 1.4, 8.3, 9.1 and 17.0 wt.% oxides, respectively) found as discrete crystals and rims on macrocrystic ilmenite; (III) perovskite significantly enriched in Na, Sr, Nb and LREE (up to 3.3, 3.4, 13.0 and 22.6 wt.% oxides, respectively) found as rims on perovskite I and II. The overwhelming majority of perovskite is represented by discrete crystals of type II. In some occurrences, this type of perovskite also has high Th contents (up to 5.5 wt.% ThO2) and Zr contents (up to 3.7 wt.% ZrO2). Textural evidence indicates that perovskite shows an overall evolutionary trend from the most primitive type I towards type III showing the highest Na, Nb and LREE contents. Perovskite of type I probably crystallized under relatively high pressures prior to the precipitation of MUM spinels. Perovskite II crystallized after magnesiochromite, pleonaste and MUM (magnesian ulvöspinel-magnetite) spinels, under increasing fO2. The most compositionally evolved type III formed during near-solidus re-equilibration of the earlier-crystallized perovskite. The compositional variation of the Lac de Gras perovskite can be adequately characterized in terms of five major end-members: CaTiO3 (perovskite), CeFeO3, NaNbO3 (lueshite), Na0.5LREE0.5TiO3 (loparite), and CaFe0.5Nb0.5O3 (latrappite).

Ion microprobe analysis ofperovskite from kimberlites and alnöites permits the accurate determination of La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er and Yb at the part per million level. Other rare earth elements (REE) are subject to interferences in the mass spectrum caused by matrix-derived molecular ions and cannot easily be determined with comparable precision. Chondrite-normalized plots of the ion probe REE data are smooth curves, confirming the superiority of this technique over electron microprobe methods at the levels of REE abundance found in these perovskites. The perovskites analysed contain between 2.8 and 7.1 wt. % REE oxides and are highly enriched in the light REE, having La/Yb ratios of 577–3229. These La/Yb ratios are not representative of the parental magmas but result from REE fractionation during crystallization of the perovskite. Parental magma La/Yb ratios are estimated to be of the order of 120–650. The lower La/Yb ratios (80–200) found for whole-rock kimberlites are considered to result from contamination by relatively heavy REE-enriched crustal material.

The octahedral-framework mineral bernalite, Fe(OH)3, provides a rare opportunity to examine directly the effects of a vacant A site upon the physical properties of perovskite-like structures. Here, we report the effect upon compressibility. Bernalite has been reported previously as having space group Immm (Birch et al., 1993), but numerous reflections violating I-centering were observed in the present study. A case is presented for bernalite having orthorhombic space group Pmmn. Lattice parameters were refined using the Le Bail method for a metrically tetragonal cell and their variation with pressure at room temperature was determined from 17 measurements at pressures from 10–4 to 9.3 GPa using synchrotron X-ray powder diffraction. No discontinuities in the compression curves of lattice parameters were observed. Fitting to a second-order Birch-Murnaghan equation-of-state (KT0' = 4) gives V0 = 438.51±0.06 Å3 and KT0 = 78.2±0.4 GPa. Second-order fits of (a/a0)3 and (c/c0)3 give elastic moduli KT0a = 82.0(6) GPa and KT0c = 71.6(4) GPa: the shorter cation–cation distance is the more compressible. These values are very close to those of stottite, FeGe(OH)6, which has tilt system a+a+c–. The difference in the elastic moduli KT0a and KT0c of bernalite and their close similarity to the stottite values support the revised Pmmn structure (tilt system a+b+c–) for bernalite proposed here. The compressional anisotropy observed in bernalite may reflect its highly anisotropic and directional H-bonding topology.

We review some of the most recent developments in classical and quantum mechanical molecular dynamics simulations, in particular as applied to Earth-forming phases at conditions prevalent in the Earth's deep interior. We pay special attention to the modelling of high pressures and temperatures, elucidating the problems associated with both the classical and quantum approaches in view of the empirical potentials required for the former, and the limitations of finite temperature calculations for the latter. We show the current status of such calculations for major phases such as MgSiO3 perovskite.

This first report of the occurrence of a kimberlitic rock in Pakistan is supported by its field relations, textures and mineral chemistry. Linear dykes, lenses, conical and pipe-like bodies, plugs and sills intrude non-orogenic, early Jurassic limestone near the SW extremity of an Eocene-emplaced ophiolite on the transform-type Indian plate margin; far away from the stable Precambrian craton. The rock resembles ‘micaceous kimberlites’ petrographically and contains olivine, phlogopite, perovskite, chromian spinel, monticellite, chlorite, serpentine, calcite, apatite, pectolite, clinopyroxene, amphibole, nepheline, magnetite and titanomagnetite. The minerals and their microprobe analyses resemble those of kimberlitic rocks.

Th- and Zr-bearing perovskite and Zr-rich Ti garnet are described from the Polino calcite carbonatite, Italy. The garnets contain 6.05-7.50 wt.% ZrO2 in cores and up to 15.80 wt.% in rims. Silicon is low in these garnets and substantial Al and Fe 3+ has been assigned to the tetrahedral sites. A strong correlation of Si with Zr from published data suggests the possibility that some Zr may also be tetrahedrally coordinated. However, the chemistry alone does not constrain the site distribution of Fe, Ti, Zr and Mg unambiguously. The perovskites are very unusual in containing 2.81-3.27 wt.% ZrO2 and 1.48-1.71 wt.% ThO2. For comparison, new analyses are presented of the zirconium garnet kimzeyite and coexisting perovskite from the type locality at Magnet Cove.

Synthetic andradite (Ca3Fe2Si3O12) has been compressed to loading pressures >21 GPa and heated to ∼1000°C by a YAG laser in a Diamond Anvil Cell (DAC). After quenching to room temperature, X-ray diffraction of the sample, still held at 21 GPa, showed that andradite had transformed to a cubic perovskite type polymorph with a = 3.460(4) Å. Upon decompression the perovskite phase transformed into an amorphous phase. The density of the perovskite polymorph (Ca3Fe2Si3O12) is ∼13.6% greater than that of isochemical andradite at 21 GPa. Ferric iron replaces Ca2+ and Si4+ in the perovskite structure (Fe3+ + Fe3+ = Si4+ + Ca2+), giving a formula unit: (Ca,Fe3+)(Si,Fe3+)O3. The new Fe3+-rich Ca-perovskite may provide new insight into the controls on the electrical conductivity of the lower mantle.