Single‐crystal growth and characterization of mullite‐type orthorhombic Bi₂M₄O₉ (M = Al³⁺, Ga³⁺, Fe³⁺)

Abstract

Pure and homogeneous single crystals of orthorhombic mullite-type Bi 2 M 4 O 9 (M = Al 3+, Ga 3+, Fe 3+), and a mixed Bi 2 Fe 1.7 Ga 2.3 O 9 crystal from an equimolar Ga/Fe composition were grown by the top seeded solution growth (TSSG) method. All these compounds melt incongruently in the range of about 800 and 1100 °C. In case of bismuth gallate and ferrate inclusion-free crystals with dimensions up to several cubic centimeters can be grown. Limited solubility in Bi 2 O 3 and the high steepness of the liquidus curve are the reasons for getting only small imperfect bismuth aluminate crystals. In contrast to ceramic materials preparation reported in literature, divalent calcium and strontium could not be incorporated into the mullite-type structure during the melt growth process. Several fundamental physical properties like heat capacity, thermal expansion, heat conductivity, elastic constants, high-pressure behavior and oxygen diffusivity were determined by different research groups using single-crystalline samples from the as-grown materials. Furthermore, the refractive indices of Bi 2 Ga 4 O 9 were measured in the range of 0.430 and 0.700 μm. Such as many other bismuth containing compounds the refractive indices of Bi 2 Ga 4 O 9 are larger than 2, and Bi 2 Ga 4 O 9 is an optic biaxial positive crystal. Dedicated to Prof. Wolfgang Neumann on the occasion of his 65th birthday

Thermal expansion of mullite-type Bi2Al4O9: A study by X-ray diffraction, vibrational spectroscopy and density functional theory

“…The CRYSTAL09 and Table 6 Selective Raman frequencies at 0 K, their corresponding mode Grüneisen parameters together with the fitting parameters used for Eqs. (12) and (13). ω i0 (cm À 1 ) ( γ i ) T A (cm À 1 ) B (cm À 1 ) Γ 0 (cm À 1 ) C (cm À 1 ) D (cm À 1 ) CASTEP based DFT calculations assign the IR and Raman vibrational modes of Bi 2 Al 4 O 9 together with a comparison between experimental observations and theoretical approaches.…”

“…Single crystals were produced by heating the Bi 2 Al 4 O 9 powder product with an excess (four times in weight) of Bi 2 O 3 at 1240 K for one day followed by cooling the melt at 2 K/h to 1210 K and held at this temperature for additional three hours. For large single crystals (mm-to cm-sized) the top seeded solution growth technique was used as described by Burianek et al [13].…”

Phase equilibria investigations and thermodynamic modeling of the system Bi2O3–Al2O3

“…Besides, the compound presents a remarkable ionic conductivity due to the presence of vacancies in oxygen lattice as it was evidenced by Abrahams et al [22]. Later, the compound was synthesized either in monocrystal form by Burianek et al [23], or by powder sintering by MacKenzie et al [24]. They measured the peritectic melting at 1084°C (by DTA) and 1050°C (by TGA/DSC in air at 10°C min À1 ) respectively.…”

Effect of Al3+ substitution on the structural, magnetic, and electric properties in multiferroic Bi2Fe4O9 ceramics

“…Gesing et al have systematically investigated the thermal expansion, stability, and elasticity properties in (Bi 1 À x Sr x ) 2 (M 1 1 À y M 2 y ) 4 O 9 À x and Bi 2 M 4 O 9 (M¼Al 3 þ , Ga 3 þ , and Fe 3 þ ). [5][6][7][8] Additionally, the extensive formation of Bi 2 M 1 4 O 9 -Bi 2 M 2 4 O 9 solid solutions provides an additional feature for the magnetic, electrical, and other materials properties which often depend on the distribution of M 1 and M 2 cations on the available octahedral and tetrahedral sites, and Weber et al have used 57 Fe Mössbauer spectroscopy of Bi 2 (Fe x M 1 À x ) 4 O 9 (M ¼Al 3 þ , Ga 3 þ ) to investigate the distribution of Fe 3 þ and Al 3 þ /Ga 3 þ in the octahedral and tetrahedral sites [9,10].…”