Rare Earth Silicates Research Articles

Crystal data for some sodium rare earth silicates

Single crystal synthesis, X-ray powder diffraction data, and electron microprobe data are given for some Na rare earth silicates of the types NaMSiO4, Na3MSi2O7, Na3MSi3O9, and Na5MSi4O12. NaYSiO4 is orthorhombic with SG Pbn21, a=5.132, b=11.156, anc c=6.405 A. NaGdSiO4 is tetragonal with SG I4 or I $$\bar 4$$ with a=11.743 and c=5.444 A. A second form of NaGdSiO4 is orthorhombic with SG P21 nb or Pmmb, a=9.179, b=27.29, and c=5.472 A. Na3YSi2O7 is hexagonal with a=9.416 and c=13.776 A. Na3YSi3O9 is orthorhombic with a=15.215, b=15.126, and c=15.036 A. Na ion conductivities of Na3YSi2O7 and Na3YSi3O9 at 300° C of 5×10−6 (Θ-cm)−1 and 6×10−6 (Θ-cm)−1, respectively, are substantially less than that for Na6YSi4O12, 1×10−1 (Θ-cm)−1.

Infrared and Raman spectra of Ca 8La 2(VO 4) 6O 2

Complex rare-earth silicate oxyapatite RE9.33(SiO4)6O2 (RE = La, Nd, Sm, Gd, Dy) ceramics have been synthesized and their thermal conduction characteristics investigated. When evaluated using a steady-state laser heat-flux technique under conditions ranging from room temperature to 1000 °C the materials demonstrated very low thermal conductivities (0.96–1.49 W m–1 K–1), especially Gd9.33(SiO4)6O2, which shows a value of 1.10–1.14 W m–1 K–1 in the measured temperature range. Phonon mean free path and Raman spectra were used to investigate the thermal transfer mechanism. The source of low thermal conductivity was determined to be the strong intrinsic scattering in the crystal cell, which is due to the phonon mean free path being on the inter-atomic level. Furthermore, a connection between the full width at half maximum Raman spectra and the thermal conductivity of RE9.33(SiO4)6O2 ceramics at room temperature was established. The insensitivity of the thermal conduction properties to temperature for RE9.33(SiO4)6O2 ceramics have allowed it to show great potential in high temperature thermal insulation applications.

New rare earth silicate crystals: Dy2MoSi2Al4O16, compounds in the systems R2O3-SiO2-PbO, and a new form of R2SiO5

The growth of crystals of a new cubic compound, Dy2MoSi2Al4O16, and of R2SiO5 (R=Dy, Tb, Gd) with a new structure is reported. Flux growth studies in the systems R2O3-SiO2-PbO are also described. These have yielded single crystals of two new families of compounds: PbR4Si5O17, with a monoclinic structure, and apatite-related phases of composition between Pb1.4Er2.93Si3.6O13 and Pb1.8Er2.5Si3.7O13 for R=Er. The compounds are characterized by X-ray powder patterns, single crystal X-ray data, and EPMA.

Flux growth of rare earth silicates and aluminosilicates

Crystals of R2SiO5, R2Si2O7, rare earth apatites, and square-faceted rare earth aluminium garnets containing silicon have been grown from fluxed melts. Silicon was provided in two ways: by vapour transport of a siliceous vapour species which diffused into the melts (“vapour-flux” method), and by including SiO2 in the initial mixtures. The results of these two methods are compared.

The determination of yttrium, europium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium in minerals by atomic-absorption spectrophotometry

A procedure is described for determining yttrium, europium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium in zirconium and calcium rare earth silicates by atomic-absorption spectroscopy, which involves the use of a lanthanum suppressor and has potential applications to other minerals containing these interferences. Although many of the associated ingredients are found to interfere, the addition of lanthanum overcomes these problems in many instances. Sensitivities and detection limits found with the proposed procedure are given for each element.

Structure and Eu 3+-fluorescence of lithium and sodium lanthanide silicates and germanates

The preparation of a series of new compounds NaLnSiO 4 and NaLnGeO 4 (Ln stands for one of the lanthanides or yttrium) is described and the results of an X-ray powder diffraction investigation of these materials are presented and discussed. Three different structure types are found for these compounds, viz. olivine, β-K 2SO 4 and an unknown structure. The compounds ALnBO 4 (A  Li, Na, B  Si, Ge, Ln  La, Gd, Y or Lu) have been doped with the Eu 3+ ion. The fluorescence of these phosphors is also reported. The spectral energy distribution of the emission gives some more information on the crystal structures. The variations of the excitation spectra and efficiencies with the crystal structure obey to correlations given by us before.

A new family of lanthanide compounds: lithium lanthanide silicates and germanates

A new family of lanthanide compounds: lithium lanthanide silicates and germanates

Preparation and properties of rare-earth silicates and aluminates

Three families of compounds between trivalent rare-earths and silica have been established; the compounds fall into three structural sub-groups. Phase equilibria of rare-earth silicates and aluminates have been investigated. Single crystals of some rare-earth silicates and aluminates have been obtained. The possibilities of applications of materials based on rare-earth silicates and aluminates have been considered and the process of dispersion hardening has been examined.

Silicates of the rare earths

1. Phase diagrams have been plotted for the binary system formed by rare earth silicates belonging to the same subgroups: $$\begin{gathered} Subgroup I\left\{ {\begin{array}{*{20}c} {La_2 O_3 \cdot 2SiO_2 - Sm_2 O_3 \cdot 2SiO_2 } \\ {2La_2 O_3 \cdot 2SiO_2 - 2Sm_2 O_3 \cdot 3SiO_2 } \\ {La_2 O_3 \cdot SiO_2 - Sm_2 O_3 \cdot 2SiO_2 } \\ \end{array} } \right. \hfill \\ Subgroup II\left\{ {\begin{array}{*{20}c} {Gd_2 O_3 \cdot 2SiO_2 - 2Dy_2 O_3 \cdot 2SiO_2 } \\ {2Gb_2 O_3 \cdot 3SiO_2 - 2Dy_2 O_3 \cdot 3SiO_2 } \\ {Gd_2 O_3 \cdot SiO_3 - Dy_2 O_3 \cdot SiO_2 } \\ \end{array} } \right. \hfill \\ \end{gathered}$$ 2. The formation of a continuous series of solid solutions has been established in the six studied systems.

An X-ray investigation of some rare-earth silicates: cerite, lessingite, beckelite, britholite, and stillwellite

SummaryAn X-ray study of a number of rare-earth silicates has been carried out; single-crystal and powder data are presented.It is found that cerites can contain up to at least 6 % CaO without disruption of the structure, which is trigonal with probable space-group P321 etc. The cell dimensions are a ca. 10·8 Å., c ca. 37–38 Å., although there is a strong pseudo-cell with halved c-axis. An ideal formula (Ca,Ln†)3Si2(O,OH,F)9 is proposed for this series.Lessingite and beckelite can be regarded chemically as lime-rich members of this cerite series. They do not, however, have the same crystal structure as cerite; their diffraction patterns are very similar to that of britholite, and indicate a structure dimensionally comparable with apatite. For a hexagonal cell, the dimensions are a ca. 9·7 Å., c ca. 7·1 Å., with probable space-group P63, &c. An ideal formula (Ca,Ln)2(Si,Al,P)(O,OH,F)5 is proposed for this series. Marked biaxial optical properties suggest that the structure may be truly orthorhombic, with a very close dimensional approximation to a hexagonal cell.The new mineral, stillwellite, is unrelated to either of these series. It is trigonal with cell dimensions a ca. 6·9 Å., c ca. 6·7 Å., with probable space-group P3112. An ideal formula (Ca,Ln)(Si,Al,P)B(O,OH,F)5 suggested by previous work is confirmed.

Mary Kathleen uranium deposit, Mount Isa-Cloncurry District, Queensland, Australia

The Mary Kathleen deposit in northwest Queensland consists of uraninite associated with allanite, in places with rare earth silicates and sulfide minerals, in intensely garnetized calc-silicate rocks forming the central unit of the Precambrian Corella beds, which have been highly dislocated and intruded by granitic rocks. The deposit is considered pyrometasomatic in origin, and the solutions responsible for garnetization and mineralization to have been late-stage emanations from the granitic magma. The uraninite has been altered to gummite, uranophane, and beta-uranotil in the zone of oxidation, which extends to a depth of about 50 feet.