High-pressure synthesis,long-term stability of single crystals of diboron trioxide,B<Subscript>2</Subscript>O<Subscript>3</Subscript>, and an empirical electronic polarizability of <Superscript>[3]</Superscript>B<Superscript>3+</Superscript>

Single crystals of B₂O₃ are needed for the precise determination of the refractive indices used to calculate the electronic polarizability α of 3-coordinated boron. The α(B) values in turn are used to predict mean refractive indices of borate minerals. Since the contribution of boron to the total polarizability of a mineral is very low, the synthetic compound B₂O₃ represents an ideal model system because of its high molar content of boron. Millimeter-sized crystals were synthesized at 1 GPa in a piston-cylinder apparatus. The samples were heated above the liquidus (800 °C), subsequently cooled at 15 °C/h to 500 °C and finally quenched. The refractive indices were determined by the immersion method using a microrefractometer spindle stage. The refractive indices n _o = 1.653 (3) and n _e = 1.632 (3) correspond to a total polarizability for B₂O₃ of α = 4.877 Å³. These values were used to determine the electronic polarizability of boron of α(B) = 0.16 Å³. Although the surface of the B₂O₃ crystals was coated with a hydrous film immediately after being exposed to air, its bulk crystallinity is retained for a period of at least 2 months.     

Thermoelastic properties of chromium oxide Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> (eskolaite) at high pressures and temperatures

A new synchrotron X-ray diffraction study of chromium oxide Cr₂O₃ (eskolaite) with the corundum-type structure has been carried out in a Kawai-type multi-anvil apparatus to pressure of 15 GPa and temperatures of 1873 K. Fitting the Birch–Murnaghan equation of state (EoS) with the present data up to 15 GPa yielded: bulk modulus (K _0,T0), 206 ± 4 GPa; its pressure derivative K′_0,T , 4.4 ± 0.8; (?K _0,T /?T) = ?0.037 ± 0.006 GPa K^?1; a = 2.98 ± 0.14 × 10^?5 K^?1 and b = 0.47 ± 0.28 × 10^?8 K^?2, where α _0,T  = a + bT is the volumetric thermal expansion coefficient. The thermal expansion of Cr₂O₃ was additionally measured at the high-temperature powder diffraction experiment at ambient pressure and α _0,T0 was determined to be 2.95 × 10^?5 K^?1. The results indicate that coefficient of the thermal expansion calculated from the EoS appeared to be high-precision because it is consistent with the data obtained at 1 atm. However, our results contradict α ₀ value suggested by Rigby et al. (Brit Ceram Trans J 45:137–148, 1946) widely used in many physical and geological databases. Fitting the Mie–Grüneisen–Debye EoS with the present ambient and high-pressure data yielded the following parameters: K _0,T0 = 205 ± 3 GPa, K′_0,T  = 4.0, Grüneisen parameter (γ ₀) = 1.42 ± 0.80, q = 1.82 ± 0.56. The thermoelastic parameters indicate that Cr₂O₃ undergoes near isotropic compression at room and high temperatures up to 15 GPa. Cr₂O₃ is shown to be stable in this pressure range and adopts the corundum-type structure. Using obtained thermoelastic parameters, we calculated the reaction boundary of knorringite formation from enstatite and eskolaite. The Clapeyron slope (with \({\text{d}}P/{\text{d}}T = - 0.014\) GPa/K) was found to be consistent with experimental data.     

Detailed comparison of nine intact rock failure criteria using polyaxial intact coal strength data obtained through PFC<Superscript>3D</Superscript> simulations

Study of intact rock failure criteria is an important topic in rock mechanics. In this study, applicability of nine different intact rock failure criteria is investigated for intact coal strength data. PFC^3D modeling was used to simulate the laboratory polyaxial tests for cubic intact coal blocks of side dimension 110 mm under different confining stress combinations. A modified grid search procedure is proposed and used to find the best-fitting parameter values and to calculate the coefficient of determination (R ²) values for each criterion. Detailed comparisons of the nine criteria are made using the following aspects: R ² values, σ ₁ ? σ ₂ plots for different σ ₃, shapes on the deviatoric plane, linearity or nonlinearity on the meridian planes. Through the comparisons of R ² values, σ ₁ ? σ ₂ plots and meridian lines, the modified Wiebols–Cook and modified Lade criteria were found to fit the intact coal strength data best. The nine failure criteria are categorized into three types based on the appearances on the deviatoric plane.     

Stability at high-pressure,elastic behaviour and pressure-induced structural evolution of CsAlSi<Subscript>5</Subscript>O<Subscript>12</Subscript>, a potential host for nuclear waste

The elastic and structural behaviour of the synthetic zeolite CsAlSi₅O₁₂ (a = 16.753(4), b = 13.797(3) and c = 5.0235(17) Å, space group Ama2, Z = 2) were investigated up to 8.5 GPa by in situ single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions. No phase-transition occurs within the P-range investigated. Fitting the volume data with a third-order Birch–Murnaghan equation-of-state gives: V ₀ = 1,155(4) ų, K _T0 = 20(1) GPa and K′ = 6.5(7). The “axial moduli” were calculated with a third-order “linearized” BM-EoS, substituting the cube of the individual lattice parameter (a ³, b ³, c ³) for the volume. The refined axial-EoS parameters are: a ₀ = 16.701(44) Å, K _T0a = 14(2) GPa (β_a = 0.024(3) GPa^?1), K′ _a = 6.2(8) for the a-axis; b ₀ = 13.778(20) Å, K _T0b = 21(3) GPa (β_b = 0.016(2) GPa^?1), K′ _b = 10(2) for the b-axis; c ₀ = 5.018(7) Å, K _T0c = 33(3) GPa (β_c = 0.010(1) GPa^?1), K′ _c = 3.2(8) for the c-axis (K _T0a:K _T0b:K _T0c = 1:1.50:2.36). The HP-crystal structure evolution was studied on the basis of several structural refinements at different pressures: 0.0001 GPa (with crystal in DAC without any pressure medium), 1.58(3), 1.75(4), 1.94(6), 3.25(4), 4.69(5), 7.36(6), 8.45(5) and 0.0001 GPa (after decompression). The main deformation mechanisms at high-pressure are basically driven by tetrahedral tilting, the tetrahedra behaving as rigid-units. A change in the compressional mechanisms was observed at P ≤ 2 GPa. The P-induced structural rearrangement up to 8.5 GPa is completely reversible. The high thermo-elastic stability of CsAlSi₅O_12, the immobility of Cs at HT/HP-conditions, the preservation of crystallinity at least up to 8.5 GPa and 1,000°C in elastic regime and the extremely low leaching rate of Cs from CsAlSi₅O₁₂ allow to consider this open-framework silicate as functional material potentially usable for fixation and deposition of Cs radioisotopes.     

Equation of state of synthetic qandilite Mg<Subscript>2</Subscript>TiO<Subscript>4</Subscript> at ambient temperature

Using a diamond-anvil cell and synchrotron X-ray diffraction, the compressional behavior of a synthetic qandilite Mg_2.00(1)Ti_1.00(1)O₄ has been investigated up to about 14.9 GPa at 300 K. The pressure–volume data fitted to the third-order Birch–Murnaghan equation of state yield an isothermal bulk modulus (K _T0) of 175(5) GPa, with its first derivative \(K_{T0}^{{\prime }}\) attaining 3.5(7). If \(K_{T0}^{{\prime }}\) is fixed as 4, the K _T0 value is 172(1) GPa. This value is substantially larger than the value of the adiabatic bulk modulus (K _S0) previously determined by an ultrasonic pulse echo method (152(7) GPa; Liebermann et al. in Geophys J Int 50:553–586, 1977), but in general agreement with the K _T0 empirically estimated on the basis of crystal chemical systematics (169 GPa; Hazen and Yang in Am Miner 84:1956–1960, 1999). Compared to the K _T0 values of the ulvöspinel (Fe₂TiO₄; ~148(4) GPa with \(K_{T0}^{{\prime }} = 4\)) and the ringwoodite solid solutions along the Mg₂SiO₄–Fe₂SiO₄ join, our finding suggests that the substitution of Mg²⁺ for Fe²⁺ on the T sites of the 4–2 spinels can have more significant effect on the K _T0 than that on the M sites.     

CO<Subscript>2</Subscript>-assisted removal of nutrients from municipal wastewater by microalgae <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> and <Emphasis Type="Italic">Scenedesmus obliquus</Emphasis>

Axenic culture of microalgae Chlorella vulgaris ATCC^® 13482 and Scenedesmus obliquus FACHB 417 was used for phycoremediation of primary municipal wastewater. The main aim of this study was to measure the effects of normal air and CO₂-augmented air on the removal efficacy of nutrients (ammonia N and phosphate P) from municipal wastewater by the two microalgae. Batch experiments were carried out in cylindrical glass bottles of 1 L working volume at 25 °C and cool fluorescent light of 6500 lux maintaining 14/10 h of light/dark cycle with normal air supplied at 0.2 L min^?1 per liter of the liquid for both algal strains for the experimental period. In the next set of experiments, the treatment process was enhanced by using 1, 2 and 5% CO₂/air (vol./vol.) supply into microalgal cultures. The enrichment of inlet air with CO₂ was found to be beneficial. The maximum removal of 76.3 and 76% COD, 94.2 and 92.6% ammonia, and 94.8 and 93.1% phosphate after a period of 10 days was reported for C. vulgaris and S. obliquus, respectively, with 5% CO₂/air supply. Comparing the two microalgae, maximum removal rates of ammonia and phosphate by C. vulgaris were 4.12 and 1.75 mg L^?1 day^?1, respectively, at 5% CO₂/air supply. From kinetic study data, it was found that the specific rates of phosphate utilization (q _phsophate) by C. vulgaris and S. obliquus at 5% CO₂/air supply were 1.98 and 2.11 day^?1, respectively. Scale-up estimation of a reactor removing phosphate (the criteria pollutant) from 50 MLD wastewater influent was also done.     

Elastic behavior of vanadinite,Pb<Subscript>10</Subscript>(VO<Subscript>4</Subscript>)<Subscript>6</Subscript>Cl<Subscript>2</Subscript>, a microporous non-zeolitic mineral

The high-pressure behavior of a vanadinite (Pb₁₀(VO₄)₆Cl₂, a = b = 10.3254(5), c = 7.3450(4) Å, space group P6₃/m), a natural microporous mineral, has been investigated using in-situ HP-synchrotron X-ray powder diffraction up to 7.67 GPa with a diamond anvil cell under hydrostatic conditions. No phase transition has been observed within the pressure range investigated. Axial and volume isothermal Equations of State (EoS) of vanadinite were determined. Fitting the P–V data with a third-order Birch-Murnaghan (BM) EoS, using the data weighted by the uncertainties in P and V, we obtained: V ₀ = 681(1) Å³, K ₀ = 41(5) GPa, and K′ = 12.5(2.5). The evolution of the lattice constants with P shows a strong anisotropic compression pattern. The axial bulk moduli were calculated with a third-order “linearized” BM-EoS. The EoS parameters are: a ₀ = 10.3302(2) Å, K ₀(a) = 35(2) GPa and K′(a) = 10(1) for the a-axis; c ₀ = 7.3520(3) Å, K ₀(c) = 98(4) GPa, and K′(c) = 9(2) for the c-axis (K ₀(a):K ₀(c) = 1:2.80). Axial and volume Eulerian-finite strain (fe) at different normalized stress (Fe) were calculated. The weighted linear regression through the data points yields the following intercept values: Fe _a (0) = 35(2) GPa for the a-axis, Fe _c (0) = 98(4) GPa for the c-axis and Fe _V (0) = 45(2) GPa for the unit-cell volume. The slope of the regression lines gives rise to K′ values of 10(1) for the a-axis, 9(2) for the c-axis and 11(1) for the unit cell-volume. A comparison between the HP-elastic response of vanadinite and the iso-structural apatite is carried out. The possible reasons of the elastic anisotropy are discussed.     

High-pressure phase transitions of CaRhO<Subscript>3</Subscript> perovskite

High-pressure phase transitions of CaRhO₃ perovskite were examined at pressures of 6–27 GPa and temperatures of 1,000–1,930°C, using a multi-anvil apparatus. The results indicate that CaRhO₃ perovskite successively transforms to two new high-pressure phases with increasing pressure. Rietveld analysis of powder X-ray diffraction data indicated that, in the two new phases, the phase stable at higher pressure possesses the CaIrO₃-type post-perovskite structure (space group Cmcm) with lattice parameters: a = 3.1013(1) Å, b = 9.8555(2) Å, c = 7.2643(1) Å, V _m  = 33.43(1) cm³/mol. The Rietveld analysis also indicated that CaRhO₃ perovskite has the GdFeO₃-type structure (space group Pnma) with lattice parameters: a = 5.5631(1) Å, b = 7.6308(1) Å, c = 5.3267(1) Å, V _m  = 34.04(1) cm³/mol. The third phase stable in the intermediate P, T conditions between perovskite and post-perovskite has monoclinic symmetry with the cell parameters: a = 12.490(3) Å, b = 3.1233(3) Å, c = 8.8630(7) Å, β = 103.96(1)°, V _m  = 33.66(1) cm³/mol (Z = 6). Molar volume changes from perovskite to the intermediate phase and from the intermediate phase to post-perovskite are –1.1 and –0.7%, respectively. The equilibrium phase relations determined indicate that the boundary slopes are large positive values: 29 ± 2 MPa/K for the perovskite—intermediate phase transition and 62 ± 6 MPa/K for the intermediate phase—post-perovskite transition. The structural features of the CaRhO₃ intermediate phase suggest that the phase has edge-sharing RhO₆ octahedra and may have an intermediate structure between perovskite and post-perovskite.     

Cosmogenic radionuclide <Superscript>7</Superscript>Be concentration in seven species of lichens and its correlation with <Superscript>40</Superscript>K, <Superscript>137</Superscript>Cs and <Superscript>226</Superscript>Ra

In this work, accumulation of cosmogenic radionuclide ⁷Be in seven species of lichens was determined using HPGe detectors in autumn season. Ramsar city which is located in the north of Iran as one of the high-level natural radiation areas in the world was considered. Lichen species represented good potential in accumulation of ⁷Be radionuclide. The foliose species of Xanthoria parietina with the highest activity concentration value of 112.8 ± 1.8 Bq kg^?1 was introduced as bioindicator for accumulation of ⁷Be radionuclide. Cladonia rangiformis species has got minimum concentration of 64.5 ± 0.8 Bq kg^?1. Also from thallus morphology viewpoint, results showed that ⁷Be accumulation in foliose species is higher than in fruticose and crustose lichens species. Also there was relatively large positive correlation between ⁷Be and ²²⁶Ra activity concentrations in lichens species.     

Sulfate Reduction and Sulfur Cycles at Two Seagrass Beds Inhabited by Cold Affinity <Emphasis Type="Italic">Zostera marina</Emphasis> and Warm Affinity <Emphasis Type="Italic">Halophila nipponica</Emphasis> in Temperate Coastal Waters

To evaluate the impact of invading seagrass on biogeochemical processes associated with sulfur cycles, we investigated the geochemical properties and sulfate reduction rates (SRRs) in sediments inhabited by invasive warm affinity Halophila nipponica and indigenous cold affinity Zostera marina. A more positive relationship between SRR and below-ground biomass (BGB) was observed at the H. nipponica bed (SRR = 0.6809 × BGB ? 4.3162, r ² = 0.9878, p = 0.0006) than at the Z. marina bed (SRR = 0.3470 × BGB ? 4.0341, r ² = 0.7082, p = 0.0357). These results suggested that SR was more stimulated by the dissolved organic carbon (DOC) exuded from the roots of H. nipponica than by the DOC released from the roots of Z. marina. Despite the enhanced SR in spring-summer, the relatively lower proportion (average, 20%) of acid-volatile sulfur (AVS) in total reduced sulfur and the strong correlation between total oxalate-extractable Fe (Fe_(oxal)) and chromium-reducible sulfur (CRS = 0.2321 × total Fe_(oxal) + 1.8180, r ² = 0.3344, p = 0.0076) in the sediments suggested the rapid re-oxidation of sulfide and precipitation of sulfide with Fe. The turnover rate of the AVS at the H. nipponica bed (0.13 day^?1) was 2.5 times lower than that at the Z. marina bed (0.33 day^?1). Together with lower AVS turnover, the stronger correlation of SRR to BGB in the H. nipponica bed suggests that the extension of H. nipponica resulting from the warming of seawater might provoke more sulfide accumulation in coastal sediments.     

Synthesis,TEM characterization and thermal behaviour of LiNiSi<Subscript>2</Subscript>O<Subscript>6</Subscript> pyroxene

A pyroxene with composition LiNiSi₂O₆ was synthesized at T = 1,473 K and P = 2.0 GPa; the cell parameters at T = 298 K are a = 9.4169(6) Å, b = 8.4465(7) Å, c = 5.2464(3) Å, β = 110.534(6)°, V = 390.78(3) Å³. TEM examination of the LiNiSi₂O₆ pyroxene showed the presence of h + k odd reflections indicative of a primitive lattice, and of antiphase domains obtained by dark field imaging of the h + k odd reflections. A HT in situ investigation was performed by examining TEM selected area diffraction patterns collected at high temperature and synchrotron radiation powder diffraction. In HTTEM the LiNiSi₂O₆ was examined together with LiCrSi₂O₆ pyroxene. In LiCrSi₂O₆ the h + k odd critical reflections disappear at about 340 K; they are sharp up to the transition temperature and do not change their shape until they disappear. In LiNiSi₂O₆ the h + k odd reflections are present up to sample deterioration at 650 K. A high temperature synchrotron radiation powder diffraction investigation was performed on LiNiSi₂O₆ between 298 and 773 K. The analysis of critical reflections and of changes in cell parameters shows that the space group is P-centred up to the highest temperature. The comparative analysis of the thermal and spontaneous strain contributions in P2₁/c and C2/c pyroxenes indicates that the high temperature strain in P-LiNiSi₂O₆ is very similar to that due to thermal strain only in C2/c spodumene and that a spontaneous strain contribution related to pre-transition features is not apparent in LiNiSi₂O₆. A different high-temperature behaviour in LiNiSi₂O₆ with respect to other pyroxenes is suggested, possibly in relation with the presence of Jahn–Teller distortion of the M1 polyhedron centred by low-spin Ni³⁺.     

Compressibility of strontium orthophosphate Sr<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> at high pressure

High pressure in situ synchrotron X-ray diffraction experiment of strontium orthophosphate Sr₃(PO₄)₂ has been carried out to 20.0 GPa at room temperature using multianvil apparatus. Fitting a third-order Birch–Murnaghan equation of state to the P–V data yields a volume of V ₀ = 498.0 ± 0.1 Å³, an isothermal bulk modulus of K _T  = 89.5 ± 1.7 GPa, and first pressure derivative of K _T ′ = 6.57 ± 0.34. If K _T ′ is fixed at 4, K _T is obtained as 104.4 ± 1.2 GPa. Analysis of axial compressible modulus shows that the a-axis (K _a  = 79.6 ± 3.2 GPa) is more compressible than the c-axis (K _c  = 116.4 ± 4.3 GPa). Based on the high pressure Raman spectroscopic results, the mode Grüneisen parameters are determined and the average mode Grüneisen parameter of PO₄ vibrations of Sr₃(PO₄)₂ is calculated to be 0.30(2).     

New insights on pressure,temperature, and chemical stability of CsAlSi<Subscript>5</Subscript>O<Subscript>12</Subscript>, a potential host for nuclear waste

A Cs-bearing polyphase aggregate with composition (in wt%): 76(1)_CsAlSi5O12 + 7(1)_CsAlSi2O6 + 17(1)_amorphous, was obtained from a clinoptilolite-rich epiclastic rock after a beneficiation process of the starting material (aimed to increase the fraction of zeolite to 90 wt%), cation exchange and then thermal treatment. CsAlSi₅O₁₂ is an open-framework compound with CAS topology; CsAlSi₂O₆ is a pollucite-like material with ANA topology. The thermal stability of this polyphase material was investigated by in situ high-T X-ray powder diffraction, the combined P–T effects by a series of runs with a single-stage piston cylinder apparatus, and its chemical stability following the “availability test” (“AVA test”) protocol. A series of additional investigations were performed by WDS–electron microprobe analysis in order to describe the P–T-induced modification of the material texture, and to chemically characterize the starting material and the run products. The “AVA tests” of the polyphase aggregate show an extremely modest release of Cs⁺: 0.05 mg/g. In response to applied temperature and at room P, CsAlSi₅O₁₂ experiences an unquenchable and displacive Ama2-to-Amam phase transition at about 770 K, and the Amam polymorph is stable in its crystalline form up to 1600 K; a crystalline-to-amorphous phase transition occurs between 1600 and 1650 K. In response to the applied P = 0.5 GPa, the crystalline-to-amorphous transition of CsAlSi₅O₁₂ occurs between 1670 and 1770 K. This leads to a positive Clapeyron slope (i.e., dP/dT > 0) of the crystalline-to-amorphous transition. When the polyphase aggregate is subjected at P = 0.5 GPa and T > 1770 K, CsAlSi₅O₁₂ melts and only CsAlSi₂O₆ (pollucite-like; dominant) and Cs-rich glass (subordinate) are observed in the quenched sample. Based on its thermo-elastic behavior, P–T phase stability fields, and Cs⁺ retention capacity, CsAlSi₅O₁₂ is a possible candidate for use in the immobilization of radioactive isotopes of Cs, or as potential solid hosts for ¹³⁷Cs γ-radiation source in sterilization applications. More in general, even the CsAlSi₅O₁₂-rich aggregate obtained by a clinoptilolite-rich epiclastic rock appears to be suitable for this type of utilizations.     

Pressure induced phase transition in Pb<Subscript>6</Subscript>Bi<Subscript>2</Subscript>S<Subscript>9</Subscript>

The crystal structure of Pb₆Bi₂S₉ is investigated at pressures between 0 and 5.6 GPa with X-ray diffraction on single-crystals. The pressure is applied using diamond anvil cells. Heyrovskyite (Bbmm, a = 13.719(4) Å, b = 31.393(9) Å, c = 4.1319(10) Å, Z = 4) is the stable phase of Pb₆Bi₂S₉ at ambient conditions and is built from distorted moduli of PbS-archetype structure with a low stereochemical activity of the Pb²⁺ and Bi³⁺ lone electron pairs. Heyrovskyite is stable until at least 3.9 GPa and a first-order phase transition occurs between 3.9 and 4.8 GPa. A single-crystal is retained after the reversible phase transition despite an anisotropic contraction of the unit cell and a volume decrease of 4.2%. The crystal structure of the high pressure phase, β-Pb₆Bi₂S₉, is solved in Pna2 ₁ (a = 25.302(7) Å, b = 30.819(9) Å, c = 4.0640(13) Å, Z = 8) from synchrotron data at 5.06 GPa. This structure consists of two types of moduli with SnS/TlI-archetype structure in which the Pb and Bi lone pairs are strongly expressed. The mechanism of the phase transition is described in detail and the results are compared to the closely related phase transition in Pb₃Bi₂S₆ (lillianite).     

The importance of defining chemical potentials,substitution mechanisms and solubility in trace element diffusion studies: the case of Zr and Hf in olivine

The diffusion, substitution mechanism and solubility limits of Zr and Hf in synthetic forsterite (Mg₂SiO₄) and San Carlos olivine (Mg_0.9Fe_0.1)₂SiO₄ have been investigated between 1,200 and 1,500 °C as a function of the chemical potentials of the components in the system MgO(FeO)–SiO₂–ZrO₂(HfO₂). The effect of oxygen fugacity and crystallographic orientation were also investigated. The solubilities of Zr in forsterite are highest and diffusion fastest when the coexisting three-phase source assemblage includes ZrSiO₄ (zircon) or HfSiO₄ (hafnon), and lower and slower, respectively, when the source assemblage includes MgO (periclase). This indicates that Zr and Hf substitute on the octahedral sites in olivine, charge balanced by magnesium vacancies. Diffusion is anisotropic, with rates along the crystal axes increasing in the order a < b < c. The generalized diffusion relationship as a function of chemical activity (as \(a_{{{\text{SiO}}_{2} }}\)), orientation and temperature is: \(logD_{\text{Zr}} = \frac{1}{4}loga_{{{\text{SiO}}_{2} }} + logD_{0} - \left( {\frac{{368 \pm 17\;{\text{kJ}}\;{\text{mol}}^{ - 1} }}{{2.303\;{\text{RT}}}}} \right)\) where the values of log D ₀ are ?3.8(±0.5), ?3.4(±0.5) and ?3.1(±0.5) along the a, b and c axes, respectively. Most experiments were conducted in air (fO₂ = 10^?0.68 bars), but one at fO₂ = 10^?11.2 bars at 1,400 °C shows no resolvable effect of oxygen fugacity on Zr diffusion. Hf is slightly more soluble in olivine than Zr, but diffuses slightly slower. Diffusivities of Zr in experiments in San Carlos olivine at 1,400 °C, fO₂ = 10^?6.6 bars are similar to those in forsterite at the same conditions, showing that the controls on diffusivities are adequately captured by the simple system (nominally iron-free) experiments. Diffusivities are in good agreement with those measured by Spandler and O’Neill (Contrib Miner Petrol 159:791–818, 2010) in San Carlos olivine using silicate melt as the source at 1,300 °C, and fall within the range of most measurements of Fe–Mg inter-diffusion in olivine at this temperature. Forsterite–melt partitioning experiments in the CaO–MgO–Al₂O₃–SiO₂–ZrO₂/HfO₂ show that the interface concentrations from the diffusion experiments represent true equilibrium solubilities. Another test of internal consistency is that the ratios of the interface concentrations between experiments buffered by Mg₂SiO₄ + Mg₂Si₂O₆ + ZrSiO₄ or Mg₂SiO₄ + ZrSiO₄ + ZrO₂ (high silica activity) to those buffered by Mg₂SiO₄ + MgO + ZrO₂ (low silica activity) agree well with the ratios calculated from thermodynamic data. This study highlights the importance of buffering chemical potentials in diffusion experiments to provide constraints on the interface diffusant concentrations and hence validate the assumption of interface equilibrium.     

Structural investigations of (Ca,Sr)ZrO<Subscript>3</Subscript> and Ca(Sn,Zr)O<Subscript>3</Subscript> perovskite compounds

(Ca _x ,Sr_1?x )ZrO₃ and Ca(Sn _y ,Zr_1-y )O₃ solid solutions were synthesized by solid-state reaction at high temperature before to be studied by powder X-ray diffraction and Raman Spectroscopy. Diffraction data allow the distortion of the ABO₃ perovskite structure to be investigated according to cations substitution on A and B-sites. It is shown that distortion, characterized by Φ, the tilt angle of BO₆ octahedra, slightly increases with decreasing y content in Ca(Sn _y ,Zr_1?y )O₃ compounds and strongly decreases with decreasing x content in (Ca _x ,Sr_1?x )ZrO₃ compounds. Such results are discussed in view of the relative A and B cation sizes. Raman data show that vibrational spectra are strongly affected by the cation substitution on A-site; the frequencies of most vibrational modes increase with increasing x content in (Ca _x ,Sr_1?x )ZrO₃ compounds, i.e. with the decreasing mean size of the A-cation; the upper shift is observed for the 358 cm^?1 mode (?ν/?r = ?60.1 cm^?1/Å). On the other hand, the cation substitution on B-sites, slightly affect the spectra; it is shown that in most cases, the frequency of vibrational modes increases with increasing y content in Ca(Sn _y ,Zr_1?y )O₃ compounds, i.e. with the decreasing mean size of the B-cation, but that two modes (287 and 358 cm^?1) behave differently: their frequencies decrease with the decreasing mean size of the B-cation, with a shift respectively equal to +314 and +162 cm^?1/Å. Such results could be used to predict the location of different elements such as trivalent cations or radwaste elements on A- or B-site, in the perovskite structure.     

Functional Performance of Three Invasive <Emphasis Type="Italic">Marenzelleria</Emphasis> Species Under Contrasting Ecological Conditions Within the Baltic Sea

A 4-week laboratory experiment investigated the behaviour (survival and bioirrigation) and impact of the invasive polychaetes Marenzelleria viridis, M. neglecta and M. arctia on sediment-water solutes exchange, porewater chemistry, and Fe and P interactions in high-salinity sandy sediment (HSS) and low-salinity muddy sediment (LSM) from the Baltic Sea. M. viridis showed deep burrowing with efficient bioirrigation (11 L m^?2 day^?1) and high survival (71%) in HSS, while M. arctia exhibited shallow burrowing with high bioirrigation (12 L m^?2 day^?1) and survival (88%) in LSM. M. neglecta behaved poorly in both ecological settings (bioirrigation, 5–6 L m^?2 day^?1; survival, 21–44%). The deep M. viridis bioirrigation enhanced total microbial CO₂ (TCO₂) production in HSS by 175% with a net efflux of NH₄⁺ and PO₄^3?, at rates 3- to 27-fold higher than for the other species. Although the shallow and intense bioirrigation of M. arctia in LSM stimulated microbial TCO₂ production to some extent (61% enhancement), the nutrient fluxes close to zero indicate that it effectively prevented the P release. Porewater Fe:PO₄^3? ratios revealed that the oxidizing effect of M. arctia bioirrigation increased the PO₄^3? adsorption capacity of LSM twofold relative to defaunated controls while no buffering of PO₄^3? was detected in M. viridis HSS treatment. Therefore, the different behaviour of the three species in various environments and the sharp contrast between M. viridis and M. arctia effects on C, N and P cycling must be considered carefully when the ecological role of Marenzelleria species in the Baltic Sea is evaluated.     

Physical properties of molecular clouds as functions of their Galactocentric distance from CS and C<Superscript>34</Superscript>S observations

Twenty-eight CS molecular clouds toward HII regions with Galactocentric distances from ～ 4 to 20 kpc have been studied based on observations obtained in the J=2→1 lines of CS and C³⁴S on the 20-meter radio telescope of the Onsala Space Observatory (Sweden) in March 2001. All 28 clouds have been mapped with an angular resolution of ～40″. The peak intensity in the C³⁴S line has been measured for 20 objects. An LTE analysis has been performed and the parameters of the molecular cloud cores derived. The core sizes are d_A=0.3–4.8 pc, with a median value of ～1.6 pc. The mean hydrogen densities in the cloud cores are n_H2=3.5×10²–3.7 × 10⁴ cm^?3, with a median value of ～7.2×10³ cm^?3. The value of n_H2 ends to decrease with increasing Galactocentric distance of the cloud. The masses of most clouds are 10²?6×10³M_⊙, with the most probable value being M_CS～10³M_⊙. The data follow the dependence M_CS ∝d _A ^(2.4–3.2) . As a rule, the cloud masses are lower than the virial masses for M_CS<10³M_⊙.     

Thermal equation of state of CaIrO<Subscript>3</Subscript> post-perovskite

The pressure–volume–temperature (P–V–T) relation of CaIrO₃ post-perovskite (ppv) was measured at pressures and temperatures up to 8.6 GPa and 1,273 K, respectively, with energy-dispersive synchrotron X-ray diffraction using a DIA-type, cubic-anvil apparatus (SAM85). Unit-cell dimensions were derived from the Le Bail full profile refinement technique, and the results were fitted using the third-order Birth-Murnaghan equation of state. The derived bulk modulus \( K_{T0} \) at ambient pressure and temperature is 168.3 ± 7.1 GPa with a pressure derivative \( K_{T0}^{\prime } \) = 5.4 ± 0.7. All of the high temperature data, combined with previous experimental data, are fitted using the high-temperature Birch-Murnaghan equation of state, the thermal pressure approach, and the Mie-Grüneisen-Debye formalism. The refined thermoelastic parameters for CaIrO₃ ppv are: temperature derivative of bulk modulus \( (\partial K_{T} /\partial T)_{P} \) = ?0.038 ± 0.011 GPa K^?1, \( \alpha K_{T} \) = 0.0039 ± 0.0001 GPa K^?1, \( \left( {\partial K_{T} /\partial T} \right)_{V} \) = ?0.012 ± 0.002 GPa K^?1, and \( \left( {\partial^{2} P/\partial T^{2} } \right)_{V} \) = 1.9 ± 0.3 × 10^?6 GPa² K^?2. Using the Mie-Grüneisen-Debye formalism, we obtain Grüneisen parameter \( \gamma_{0} \) = 0.92 ± 0.01 and its volume dependence q = 3.4 ± 0.6. The systematic variation of bulk moduli for several oxide post-perovskites can be described approximately by the relationship K _T0  = 5406.0/V(molar) + 5.9 GPa.