High-Pressure Synthesis, Crystal Structure, and Properties of the New Orthorhombic Rare-Earth meta-Oxoborates RE(BO₂)₃ (RE = Dy – Lu)

Abstract

The new orthorhombic meta-oxoborates RE(BO2)3 (≡REB3O6) (RE = Dy-Lu) have been synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C. They are isotypic to the known ambient pressure phase Tb(BO2)3, space group Pnma. In contrast to Dy(BO2)3, which was also obtained in small amounts under high-temperature conditions, the preparation of the higher orthorhombic homologues RE(BO2)3 (RE = Ho-Lu) was only possible using high-pressure. The meta-oxoborates RE(BO2)3 (RE = Dy-Er) were synthesized as pure products, whereas the orthorhombic phases with RE = Tm-Lu were only obtained as byproducts. With the exception of Yb(BO2)3 it was possible to establish single crystal data for all compounds. The results of temperature-resolved in-situ powder-diffraction measurements, DTA, IR-spectroscopic investigations, and magnetic properties are also presented.

Ce2B8O15: High-pressure synthesis and crystal structure determination of a rare-earth polyborate exhibiting a new “Fundamental Building Block”

“…The varying B-O bond lengths result in moderately distorted BO 4 tetrahedra in the crystal structure of Ce 2 B 8 O 15 . The elongated bond length of threefold coordinated oxygen to boron atoms have already been observed in few minerals, synthetic oxoborates, but especially in high-pressure phases like b-MB 4 O 7 (M ¼ Mn, Fe, Co, Ni, Cu, Zn) [25][26][27], the metaborates b-, g-, and d-RE(BO 2 ) 3 [7][8][9][28][29][30], and the high pressure modification of B 2 O 3 [31]. The corresponding average B-O distances in these compounds range around 153 pm [32].…”

Polymorphy of monoclinic terbium triborate, TbB3O6

“…Later on, using lithium borate flux, crystals of REB 3 O 6 with RE = Dy -Tm could be synthesized in our group at ambient pressure at temperatures between 850°C and 750°C in air atmosphere. The orthorhombic (Pnma) crystal structure of these compounds, as given by [17], was corroborated by Rietveld refinement of X-ray powder diffraction data (collected on a Philips PW 1800 diffractometer), an example for DyB 3 O 6 is given in figure 1. In this work we report on a study of monoclinic TbB 3 O 6 , that is found to adopt either a low-temperature or a high-temperature modification.…”

“…Tb is eightfold coordinated by oxygen ligands and is arranged in strongly corrugated layers parallel (100). Triborate compounds of the smaller lanthanides, Dy -Lu, were obtained as orthorhombic crystals with space group symmetry Pnma by high-pressure synthesis at 7.5 GPa and 1000°C [17]. Together with orthorhombic TbB 3 O 6 they form a second isomorphic series among the REB 3 O 6 .…”

Crystal structure of dysprosium meta-oxoborate, β-Dy(BO2)3, via normal-pressure synthesis

“…Two highpressure high-temperature modifications were recently synthesized: the orthorhombic g-M(BO2)3-type (M = La -Nd, Pca21) [2] and the monoclinic d-La(BO2)3-type compounds (P21/c) [3]. For the first time, an example of the fourth known phase of metaoxoborates, b-Tb(BO2)3 was obtained under normal-pressure high-temperature conditions [4], whereas single crystals of b-M(BO2)3 with M = Dy -Lu [5] …”