Ca3Ga2Ge4O14 Structure Research Articles

Correlation between the Parameters of the Dispersion Relations of Refractive Indices and Coordination Numbers of Cations for the Langasite-Family Crystals

Correlation between the parameters of the dispersion relations of refractive indices and coordination numbers of cations in the structure is found for langasite-family La3Ga5SiO14 optical crystals (C-a3Ga2Ge4O14 structure type, sp. gr. P321).

Formation of Phases with the Ca3Ga2Ge4O14 Structure in Ln2O3–M2O3–GeO2–BeO (Ln = La–Gd, M = Ga, Al, Fe, Cr) Systems

Phases of variable composition Ln3M5 – 2xGe1 + xBexO14 (Ln = La–Gd; M = Ga, Al, Fe, Cr) with the Ca3Ga2Ge4O14 (GGG) structure (space group P321) were prepared by solid-phase synthesis at 1100–1400°С. In Ga systems, GGG phases are formed for La–Eu; in Al systems, for La–Gd; for Fe, only in the La system; and in Cr systems, for La–Sm. Ln3CrGe3Be2O14 compounds have an ordered crystal structure with oxygen octahedra occupied by Cr3+ ions. The other phases have an M–Ge–Be disordered structure. The compounds are decomposed in a solid phase and (or) melt incongruently.

Optical spectroscopy of a La3Ga5SiO14:Co2+ crystal

The absorption, luminescence, and circular dichroism spectra of a cobalt-doped La3Ga5SiO14 crystal (Ca3Ga2Ge4O14 structure, sp. gr. P321) have been studied in the range 8–300 K. The Co2+ ion has been shown to occupy the 3f tetrahedral site. For T 220 K, the 2E(2G) state is completely quenched, and only luminescence from the 4T1(4P) level is observed.

Formation of phases with the Ca3Ga2Ge4O14 structure in the AO-TeO3-Ga2O3-XO2 (A = Pb, Ba, Sr; X = Si, Ge) and PbO-TeO3-MO-GeO2 (M = Zn, Co) systems

Variable-composition phases with the Ca3Ga2Ge4O14 structure with a wide homogeneity region were synthesized in quaternary silicate and germanate systems. In (Pb,Ga)-containing systems, sections of the homogeneity region were studied and their boundaries were determined. Cationic vacancies were found. In the 3e position, their concentration can be as high as 25%. The synthesized phases melt incongruently or experience solid-phase decomposition.

New compounds A 3 + Te6+M 3 3+ X 2 5+ O14 (A = Na, K; M = Ga, Al, Fe; X = P, As, V) with the Ca3Ga2Ge4O14 structure

Compounds A3+Te6+M33+X25+O14 (A = Na, K; M = Ga, Al, Fe; X = P, As, V) with the Ca3Ga2Ge4O14 structure (sp. gr. P321) were prepared by solid-phase synthesis at 600–850°C in air. The compounds melt incongruently or decompose in the solid state.

Synthesis of dugganite Pb3TeZn3As2O14 and its analogues

A32+Te6+M32+ X25+O14 (A = Pb, Ba, Sr; M = Zn, Mg, Co, Mn, Cu, Cd; X = P, As, V) compounds and Pb3WZn3P2O14, all with Ca3Ga2Ge4O14 structure (space group P321), were prepared by solid-phase synthesis in air at 600–1000°C. Most compounds melt incongruently or experience solid-phase decomposition.

Antiferromagnetic Ordering of the 3d Ions in Compounds with Ca<sub>3</sub>Ga<sub>2</sub>Ge<sub>4</sub>O<sub>14</sub> Structure

Compounds with the Ca3Ga2Ge4O14 structure containing Co2+, Mn2+ and Fe3+ ions in 3f position were synthesized and their magnetic properties were studied at low temperatures. Long range antiferromagnetic ordering in triangular net lattice has been observed with TN = 7–40 K.

Phase transitions in compounds with the Ca3Ga2Ge4O14 structure

Possible structural changes described by the group-subgroup relationships in the Ca3Ga2Ge4O14-type structure (sp. gr. P321) are considered. The most probable phase transitions seem to be those accompanied by lowering of the symmetry to the maximal non-isomorphic subgroups P3 and C2. It is shown that only destructive phase transitions accompanied by symmetry rise up to the minimal non-isomorphic supergroups for the given structure type can take place. The change of the trigonal symmetry to monoclinic is revealed in La3SbZn3Ge2O14, whose crystal structure is refined as a derivative structure of the Ca3Ga2Ge4O14 structure type within the sp. gr. A2 (C2). At ∼250°C, La3SbZn3Ge2O14 undergoes a reversible phase transition accompanied by symmetry rise, A2 ⇄ P321. Similar phase transitions, P321 ⇄ A2, are also observed in La3Nb0.5Ga5.5O14 and La3Ta0.5Ga5.5O14 under the hydrostatic pressures 12.4(3) and 11.7(3) GPa, respectively. The mechanisms of compression and phase transition are based on the anisotropic compressibility of a layer structure. With the attainment of the critical stress level in the structure, the elevated compressibility in the (ab) plane gives rise to a phase transition accompanied by the loss of the threefold axis. Attempts to reveal low-temperature phase transitions in a number of representatives of the langasite family have failed.

Growth and structure of La3Zr0.5Ga5Si0.5O14 crystals

The complete X-ray structure determination of Czochralski grown La3Zr0.5Ga5Si0.5O14 single crystals with the Ca3Ga2Ge4O14 structure is performed (sp. gr. P321, a = 8.226(1) A, c = 5.1374(6) A, Z = 1, Mo Kα1 radiation, 1920 crystallographically independent reflections, R = 0.0166, Rw = 0.0192). The absolute structure is determined. It is shown that possible transition of some of La atoms (∼1.2%) from the 3e to 6g position may give rise to the formation of structural defects.

Acentric disordered Nd3+:La3Ga5SiO14 crystal. A broadband luminescence material with high thermal conductivity to generate picosecond laser pulses

The disordered acentric Nd3+ : La3Ga5SiO14 crystal with trigonal Ca3Ga2Ge4O14 structure is tested in an actively and passively mode-locked laser system, which generates stable single pulses of 5.8 ps duration at pulse energy 250 μJ and wavelength λ = 1067 nm (4F3/2 4I11/2 laser channel). The pulse repetition rate can be increased to above 10 Hz. The disordered laser crystal delivers comparable output energy with higher stability compared with phosphate laser Nd3+ :glass. Some important physical properties of La3Ga5SiO14 are considered.