Crystallochemical Design of Huntite-Family Compounds

Abstract

Huntite-family nominally-pure and activated/co-activated LnM3(BO3)4 (Ln = La–Lu, Y; M = Al, Fe, Cr, Ga, Sc) compounds and their-based solid solutions are promising materials for lasers, nonlinear optics, spintronics, and photonics, which are characterized by multifunctional properties depending on a composition and crystal structure. The purpose of the work is to establish stability regions for the rare-earth orthoborates in crystallochemical coordinates (sizes of Ln and M ions) based on their real compositions and space symmetry depending on thermodynamic, kinetic, and crystallochemical factors. The use of diffraction structural techniques to study single crystals with a detailed analysis of diffraction patterns, refinement of crystallographic site occupancies (real composition), and determination of structure–composition correlations is the most efficient and effective option to achieve the purpose. This approach is applied and shown primarily for the rare-earth scandium borates having interesting structural features compared with the other orthoborates. Visualization of structures allowed to establish features of formation of phases with different compositions, to classify and systematize huntite-family compounds using crystallochemical concepts (structure and superstructure, ordering and disordering, isostructural and isotype compounds) and phenomena (isomorphism, morphotropism, polymorphism, polytypism). Particular attention is paid to methods and conditions for crystal growth, affecting a crystal real composition and symmetry. A critical analysis of literature data made it possible to formulate unsolved problems in materials science of rare-earth orthoborates, mainly scandium borates, which are distinguished by an ability to form internal and substitutional (Ln and Sc atoms), unlimited and limited solid solutions depending on the geometric factor.

Structural, Electronic and Vibrational Properties of YAl3(BO3)4

“…The typical Infrared spectra of huntite-like ReM 3 (BO 3 ) 4 (Re = Y, rare-earth element, M = Al, Ga, Fe, Cr) compounds with noncentrosymmetric trigonal structure (R32 space group) should contain an empty gap in the range 1050-1200 cm −1 [62][63][64]. However, as discussed earlier [65][66][67], the borates with large rare-earth elements can form not only trigonal but also monoclinic structures depending on the growth conditions. Some extra bands (in comparison with trigonal structure) were observed in the range of 1050-1200 cm −1 and these bands assigned to ν 3 vibrations of BO 3 3− ions [67,68].…”

Phase transitions and p–T phase diagram of the multiferroic TbFe3(BO3)4 crystal

“…[5][6][7] The possibility of practical application and the prospect of creating new solid solutions by partial replacement of rare-earth ions or iron ions attract researchers. [1,3,[7][8][9][10][11] However, to create new materials, it is necessary to carefully study the base crystal properties.…”

Фазовая диаграмма и особенности поведения мягких мод в твердых растворах со структурой хантита TbFe-=SUB=-3-x-=/SUB=-Ga-=SUB=-x-=/SUB=-(BO_3)-=SUB=-4-=/SUB=-

“…Кристаллы редкоземельных ферроборатов со структурой хантита [1] являются перспективными материалами для оптоэлектронных устройств. Например, в этом семействе обнаружены кристаллы с большими значениями магнитоэлектрического эффекта [2].…”