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1.
Four crystals of synthetic wadsleyite, -(Mg,Fe)2SiO4, were mounted together in one diamond-anvil cell for the determination of unit-cell parameters as a function of pressure. The Fe/(Fe+Mg) are 0.00, 0.08, 0.16, and 0.25 (the most iron-rich stable composition). Unit-cell refinements were made at 12 pressures up to 4.5 GPa. No phase transitions were observed and all crystals remained dimensionally orthorhombic. Of the three axes, c is the most compressible (0.000239(3) GPa-1), whereas compressibilities of a and b are both about 30% less. The Fe content has no systematic effect on volume or linear compressibilities. Bulk moduli, based on a Birch-Murnaghan equation of state (K assumed to be 4.00) are 160(3), 169(3), 164(2), and 165(3) GPa for the four crystals in order of increasing Fe. Substitution of Fe for Mg, therefore, does not appear to have a systematic effect on bulk modulus. Other factors, especially Fe3+/Fe2+ and other deviations from the strict Mg2SiO4-Fe2SiO4 binary, may have a greater influence on compressibility. 相似文献
2.
F. Hatert 《Mineralogy and Petrology》2004,81(3-4):205-217
Summary Phosphates of compositions (Na1–xLix)1.5Mn1.5Fe1.5(PO4)3 were synthesized by solid state reactions in air, and pure alluaudite-type compounds were obtained for x=0.00, 0.25, and 0.50. Rietveld refinements of X-ray powder diffraction data indicate the occurrence of Mn2+ in the M(1) site, and of Fe3+ and Mn2+ in the M(2) site. For x=0.25 and 0.50, A(1) is occupied by Li+ and Na+, whereas A(2) is occupied by Na+ and vacancies. A careful examination of the number of electrons occurring in the A sites of the alluaudite-type compounds (Na1–xLix)MnFe2(PO4)3 and (Na1–xLix) CdIn2(PO4)3 confirms that lithium occupies only the A(1) crystallographic site of the alluaudite structure. 相似文献
3.
R. H. Mitchell A. R. Chakhmouradian P. M. Woodward 《Physics and Chemistry of Minerals》2000,27(8):583-589
Perovskite-type compounds in the series tausonite-loparite, (Sr1?2 x Na x La x )TiO3, were synthesized by solid-state reaction (final heating at 1200–1300?°C), and studied using “conventional” and synchrotron X-ray powder diffractometry. The structures of intermediate compositions were determined using the Rietveld profile refinement method. In the compositional range 0?≤x?≤ 0.1, the series comprises perovskites characterized by an undistorted cubic structure (space group Pm3¯m, a?≈ 3.905–3.902?Å, Z?=?1). Intermediate compounds in the range 0.15?≤?x?≤?0.35 crystallize with tetragonal symmetry (I4/mcm, a?≈? , c?≈? , Z?=?4) derived from the cubic aristotype by antiphase rotation of the TiO6 octahedra about a fourfold axis. The angle of rotation estimated from the positional parameters of oxygen atoms ranges from 2.5(7)° to 5.5(4)°. The cubic-to-tetragonal transition arises from substitution of Sr2+ by the comparatively smaller Na1+ and La3+ cations. A further transition from the tetragonal to rhombohedral symmetry (R3¯c, a?≈? , c?≈?2 , Z?=?6) occurs between x?=?0.35 and 0.40, and apparently does not involve formation of perovskite with an intermediate two-tilt structure (Imma). The rhombohedral structure is characterized by a multicomponent octahedral tilt about a threefold axis ranging in magnitude from 6.5(2)° to 7.7(2)°. In the series (Sr1?2 x Na x La x )TiO3, the unit-cell dimensions decrease, and the degree of structural distortion increases with x. 相似文献
4.
O. Noked A. Melchior R. Shuker S. Chizawa H. P. Liermann B. J. Kennedy M. Nakayama E. Sterer 《Physics and Chemistry of Minerals》2014,41(5):333-340
The high-pressure behavior of Li x La1/3NbO3 (x = 1/6, 1/3, 1/2, 2/3) perovskites where Li cations were substituted for the existing vacancies was studied using synchrotron X-ray diffraction. It was shown that all these materials undergo irreversible pressure-induced amorphization around 14.5 GPa regardless of the Li concentration. The Li-inserted materials were found to exhibit a standard pressure response (bulk modulus pressure derivative B 0′ ~4) when in the crystalline phase, whereas La1/3NbO3 shows a linear volume contraction versus pressure, i.e., B 0′ ~(?1). These results suggest that the structural collapse is not a consequence of cation disorder resulting from the Nb atoms (B-site) migrating to the A-site vacancies. The observed pressure response can be understood by increased occupancy of the A-sites opposing the tilting of the NbO6 octahedra. The pressure evolution of the Nb oxidation state is discussed. 相似文献
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Gianluca Iezzi Zhenxian Liu Giancarlo Della Ventura 《Physics and Chemistry of Minerals》2009,36(6):343-354
The high-pressure behavior of three synthetic amphiboles crystallized with space group P21/m at room conditions in the system Li2O–Na2O–MgO–SiO2–H2O has been studied by in situ synchrotron infrared absorption spectroscopy. The amphiboles have compositions ANa B(Na
x
Li1 − x
Mg1) CMg5 Si8 O22(OH)2 with x = 0.6, 0.2 and 0.0, respectively. The high-P experiments up to 32 GPa were carried out on the U2A beamline at Brookhaven National Laboratory (NY, USA) using a diamond
anvil cell under non-hydrostatic or quasi-hydrostatic conditions. The two most intense absorption bands in the OH-stretching
infrared spectra can be assigned to two non-equivalent O–H dipoles in the P21/m structure, bonded to the same local environment M1M3Mg3–OH–ANa, and pointing toward two differently kinked tetrahedral rings. In all samples these bands progressively merge to give a
unique symmetrical absorption with increasing pressure, suggesting a change in symmetry from P21/m to C2/m. The pressure at which the transition occurs appears to be linearly correlated to the aggregate B-site dimension. The infrared
spectra collected for amphibole B(Na0.2Li0.8Mg1) in the frequency range 50 to 1,400 cm−1 also show a series of changes with increasing pressure. The data reported here support the inference of Iezzi et al. (Am
Miner 91:479–482, 2006a) regarding a new high-pressure amphibole polymorph. 相似文献
8.
Masaki Akaogi Nanami Horiuchi Takayuki Ishii Hiroshi Kojitani 《Physics and Chemistry of Minerals》2012,39(10):797-802
Phase relations in the system TiO2–ZrO2 were examined in the pressure range of 3.5–12?GPa at 1,800?°C, using multianvil apparatus. At 1,800?°C, TiO2 rutile transforms to αPbO2 structure at 10?GPa, and the αPbO2-type solid solution is stable in compositional range between TiO2 and about (Ti0.6, Zr0.4)O2 at 3.5–12?GPa. Combination of the present results with the published data at 0–3?GPa demonstrates that continuous solid solution with the αPbO2-type structure is stable between TiO2 and (Ti1?x , Zr x )O2 (x?≈?0.6) at 0–12?GPa. This indicates that both the αPbO2-type TiO2 and srilankite Ti2ZrO6 with the same structure belong to the continuous solid solution system though the two phases have been regarded as different minerals. With increasing ZrO2 content, lattice parameters of a- and c-axes of the αPbO2-type solid solution increase, but b-axis is almost constant or slightly decreases. At higher pressure, the αPbO2-type solid solution dissociates into two phases, αPbO2-type phase and tetragonal zirconia. Srilankite with more TiO2-rich composition than Ti2ZrO6 might be found in natural rocks derived from the deep upper mantle. 相似文献
9.
The crystal structures of the two hydrous wadsleyite crystals with formulae, Mg1.75SiH0.50O4 (0.5H–β) and Mg1.86SiH0.28O4 (0.3H–β) have been analyzed in this study. The single-crystal X-ray diffraction data showed that the unit cells of the 0.3H–β
and the 0.5H–β are metrically monoclinic with a slight distortion from the orthorhombic cell but their intensity distributions
conform to the orthorhombic symmetry within the limit of experimental errors. The Fourier and the difference Fourier syntheses
were calculated. Small but significant Fourier peaks were found at the site, Si2, in a normally vacant tetrahedral void adjacent
to Mg3 site as reported for the monoclinic hydrous wadsleyite by Smyth et al.. From the comparison of the hydrous and anhydrous
wadsleyite structures, the Mg-vacant structural modules were found to be the building units for the structure of hydrous wadsleyite.
The dilution of symmetry from orthorhombic to monoclinic in the hydrous wadsleyite structure is interpreted qualitatively
due to lack of mirror perpendicular to the a axis in the module. The mode of arrangement of the Mg-vacant structural modules
interprets the symmetry and hydrogen content of the hydrous wadsleyite and gives the structural relationship between hydrous
wadsleyite and hydrous ringwoodite.
Received: 8 May 1998 / Revised, accepted: 3 October 1998 相似文献
10.
A. R. Chakhmouradian K. Ross R. H. Mitchell I. Swainson 《Physics and Chemistry of Minerals》2001,28(4):277-284
A series of fluoride perovskites related to neighborite was investigated using X-ray and neutron diffraction techniques, and Rietveld profile refinement of powder diffraction data. The series (Na1? x K x )MgF3 comprises orthorhombic (Pbnm, a?≈? , b?≈? , c?≈?2a p , Z=4) perovskites in the compositional range 0?≤?x?≤?0.30, tetragonal perovkites (P4/mbm, a?≈? , c?≈?a p , Z=2) in the range 0.40?≤?x?≤?0.46, and cubic phases (Pm3¯m, Z=1) for x?>?0.50. The structure of the orthorhombic neighborite is derived from the perovskite aristotype by rotation of MgF6 octahedra about the [110] and [001] axes of the cubic subcell. The degree of rotation, measured as a composite tilt Φ about the triad axis, varies from 18.2° at x=0 to 11.2° at x=0.30 (as determined from the fractional atomic coordinates). Orthorhombic neighborite also shows a significant displacement of Na and K from the “ideal” position (≤0.25?Å). The tetragonal members of the neighborite series exhibit only in-phase tilting about the [001] axis of the cubic subcell (φ) ranging from 4.5° to 4.8° (determined from the atomic coordinates). The solid solution (Na1? x K x )MgF3, shows a regular variation of unit-cell dimensions with composition from 3.8347?Å for the end-member NaMgF3 (reduced to pseudocubic subcell, a p ) to 3.9897?Å for KMgF3. This variation is accompanied by increasing volumes of the A-site polyhedra, whereas the volume of MgF6 octahedra initially decreases (up to x=0.40), and then increases concomitantly with K content. The polyhedral volume ratio, V A /V B , gradually increases towards the tetragonal structural range, in agreement with diminishing octahedral rotation in the structure. The P4/mbm-type neighborite has an “anomalous” polyhedral volume ratio (ca. 5.04) owing to the critical compression of MgF6 polyhedra. 相似文献
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根据鄂尔多斯盆地神木煤田延安组1~(-1)、1~(-2)及2~(-2)煤层的平均光泽和结构特征,划分出了12种宏观煤岩类型。显微研究表明,该区煤中均质镜质体的含量较高,且多为草本植物和灌木类所组成,因此认为根皮镜质体的大量存在是该区煤的主要煤岩特征之一。此外,一些过渡型显微组分,如半镜质体和半丝质体的含量也相对高。依据因子分析和聚类分析结果并结合凝胶化指数和结构保存指数,划分出4种沼泽相:开阔水域水生植物淤泥相、深覆水草甸沼泽相、浅覆水草本灌木混生沼泽相和陆地森林沼泽相。 相似文献
12.
Diffuse X-ray scattering distributions have been recorded for reciprocal layers normal to c
* of a synthetic mullite with composition Al2(Al2+2xSi2–2x) O10–xx, where represents an oxygen vacancy and x is close to 0.4. The effect on the diffuse scattering pattern of different schemes for ordering of the oxygen vacancies and the accompanying cation shifts within a single ab-layer of mullite has been investigated using optical diffraction analogue experiments in conjunction with Monte Carlo simulation.A simple scheme in which the only driving force for the ordering is that the Oc oxygens are precluded from being bonded to four T/T* cations, results in a 2D diffuse intensity distribution which displays many of the features that are observed in the x-ray scattering patterns. An alternative scheme in which bonding to four T/T* cations was favoured, resulted in a domain structure consisting of islands of the -alumina structure within a matrix of sillimanite. This gave diffraction patterns bearing no resemblance to the observed x-ray patterns and can, we believe, be discounted completely. 相似文献
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蒋仁 《水文地质工程地质》1983,(3)
水化学成份中pH、CO_3~(2-)、HCO_3~(1-)、Ca~(2 )和Mg~(2 )的测定,是水分析中通常要测定的常规项目。习惯上用一份溶液测定pH,一份溶液测定CO_3~(2-),另一份溶液测定HCO_3~(1-),Ca~(2 )叶和Mg~(2 )。我们采用酸度计指示终点的电位滴定法。在同一份溶液中测定pH、CO_3~(2-)、和HCO_3~(1-),然后再用EDTA络合滴定Ca~(2 )和Mg~(2 )。方法简便快速,准确可靠。 相似文献
15.
Three (Cr1?x Al x )N (x = 0.33, 0.5, 0.66) coatings were deposited on Ni-super alloy IN718 using reactive magnetron sputtering. The oxidation behavior of all coatings at 900 °C up to 500 h in air was studied. Furthermore, the corrosion behavior of the (Cr0.33,Al0.66)N coating at 900 °C (corrosion type I) by spraying a uniform salt scale of Na2SO4 on the sample surface (1 mg/cm2) was investigated. It was found that the coated samples indicate significantly higher oxidation and corrosion resistance compared to uncoated Ni super alloy. This is mainly due to the formation of protective Cr2O3 and Al2O3 layers on the coating surface. With the increase of Al content, the coatings exhibited improved oxidation resistance. The formation of thin and adherent Al2O3 scale on the surface of Al rich coating is the reason for its better oxidation behavior. The detailed structures of the oxide scales and the interdiffusion between coating and substrate were studied using energy dispersive X-ray spectroscopy-analysis. 相似文献
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刁飞一ISON WITH THOSE OF NEIGHBORINGAREAS(AMCS,ISSN 1000一0674,CN32一1 1 89,12(4),1995,p.349一373,2 graPhs,4tables,35 ref,wirh English abstraet)962146 Shang Ping(Fuxin Institute of Mi-n ing and‘I’eehnology,Fuxin,Liaoning)THE NATURE AND CHARACTERS OFTHE EARLY CRETACEOUS FLORAFROM THE PINGZHUANG BASIN,IN-NER MONGOLIA(GR,ISSN 0371一5736,CN 11一1 952/P,41(6),1995,P.533一536,1table,6 ref,with English abstraer)962144 Tong Guobang(Institute o… 相似文献
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980326 Chen Jianqiang(China University ofGeoseienees,Beijing)The MicroskeletalStruCtUreS ofM公k耐t勿LavruseviCh(Rugosa)(Aeta Palaeontologieal Siniea,ISSN 0001一6616,CN 32一1188,36(4),1 997,p.446一452,2 tables,2 Plates,18ref) Maikottia Lavrusevieh 1 967 15 a group ofPeeuliar fossil eystiPhyllids,usually in eerioideompound forms with eystiPhylloid septa eom-posed of eomposite rhabdaeanthines,rangingfrom Lower Silurian(Llandovery series)toUPPer Silurian(Ludlow series)in theYangtze … 相似文献
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971349 Che;19 Jie(China Universityseienees,Beijing)The MammaljanShowjng ClimatieF盆uetuat应on—ExamPle of the Early Pleistoceneof Ge。FaunaS AS anMam-malian Faunas from Zhoukoudian,Beijing,China(ESI矛,ISSN 1 005一2321,CN 11一3370/P,4(2),1997,p·275一279,1 graph,1 table,10 ref) By analyses of the four local marnmalianfaunas from Zhoukoudian,Beijing,the EarlyPleistoeene elimatie and eeologieal environ-CN 11一1 905/Q1 53,1 graph,1735(2).1997,P.145一mental ehangespaper.One of1 .90M… 相似文献
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980302 Feng Heng(块Partment of Earth Sci-enees,Nanjing University,Nanjing,J iangsu);Yang Xiangning Study on Taxono--my of Some PSeudOSchwageri加(FusulinidForamln三fera)(Aeta MieropalaeontologieaSiniea,ISSN 1000一0674,CN32一1189,14(3),1997,p.280一294,5 graphs,1 table,2 Plates,24 ref) Morphologieal measurements of 123 thinsections and sPeeimens Published in the litera-ture have been used to study the taxonomy of厂、6心oschwagerina“dd翻1 Dunbar et Skin-ner, 1 937,P.洲烤口ris(Scher肠… 相似文献