In Situ Vibration Spectroscopy was Used to Reveal the Microstructure Evolution Mechanism of Iron Garnet Single Crystal Growing from Multi-component Oxides Melt

Abstract

Rare-earth iron garnets (ReIGs), performance depends on lattice integrity and heteroatomic substitution sites. However, the lack of growth mechanisms in mainstream processes (such as LPE) limits the quality control and the understanding of atomic occupancy preferences of ReIGs. Herein, the use of density functional theory (DFT) and in situ Raman spectroscopy to reveal the microstructure geometry and self-assembly mechanism of (TbBi)3FeO5O12 based melts [(Fe2O3‒Tb4O7‒Bi2O3), 1; (Fe2O3‒Tb4O7‒Bi2O3‒B2O3), 2]. The results show that both 1 and 2 show anion and cation cluster characteristics with multi-level size distribution, in which four-metal chainlike clusters [Fe(III)On‒AO2‒Fe(III)O2‒AOm][4-2(m+n)]- [A = Tb3+ or Bi3+; n (m) = 2 and 3] are confirmed to be the growth units of ReIGs due to their dominant components in the melt. Notably, solidification kinetics show that the growth units of 1 restructure periodic long-chains [‒AO2‒Fe(III)O2‒]n2n- during cooling. Electrostatic potential analysis shows that ReIG crystals follow the axial extension of [Fe(III)On‒AO2‒Fe(III)O2‒AOm][4-2(m+n)]- and achieve three-dimensional dynamic assembly through electrostatic bonding with free Fe³⁺. In addition, B2O3 hardly changes the intrinsic structures of the high-temperature melt and maintains stability by enhancing the interaction between clusters. This work illustrates the self-assembly mechanism of ReIGs crystal growth from the atomic scale, providing new insights for the optimization of single crystal performance by regulating the melt structure.