Optical Floating Zone Crystal Growth of Rare-Earth Disilicates, R₂Si₂O₇ (R = Er, Ho, and Tm)

Abstract

The wealth of structural phases seen in the rare-earth disilicate compounds promises an equally rich range of interesting magnetic properties. We report on the crystal growth by the optical floating zone method of members of the rare-earth disilicate family, R 2 Si 2 O 7 (with R = Er, Ho, and Tm). Through a systematic study, we have optimized the growth conditions for Er 2 Si 2 O 7 . We have grown, for the first time using the floating zone method, crystal boules of Ho 2 Si 2 O 7 and Tm 2 Si 2 O 7 compounds. We show that the difficulties encountered in the synthesis of polycrystalline and single crystal samples are due to the similar thermal stability ranges of different rareearth silicate compounds in the temperature−composition phase diagrams of the R-Si-O systems. The addition of a small amount of SiO 2 excess allowed the amount of impurity phases present in the powder samples to be minimized. The phase composition analysis of the powder X-ray diffraction data collected on the as-grown boules revealed that they were of single phase, except in the case of thulium disilicate, which was comprised of two phases. All growths resulted in multigrain boules, from which sizable single crystals could be isolated. The optimum conditions used for the synthesis and crystal growth of polycrystalline and single crystal R 2 Si 2 O 7 materials are reported. Specific heat measurements of erbium and thulium disilicate compounds confirm an antiferromagnetic phase transition below T N = 1.8 K for D-type Er 2 Si 2 O 7 and a Schottky anomaly centered around 3.5 K in C-type Tm 2 Si 2 O 7 , with an upturn in C(T)/T below 1 K suggesting the onset of short-range magnetic correlations. Magnetic susceptibility data of E-type Ho 2 Si 2 O 7 reveals an antiferromagnetic ordering of the Ho spins below T N = 2.3 K.

Ba9RE2(SiO4)6 (RE = Ho–Yb): A Family of Rare-Earth-Based Honeycomb-Lattice Magnets

“…The search for Kitaev QSL states in real materials has been extensively performed on the honeycomb-lattice magnets comprising the 4d/5d transition-metal ions due to the bond-dependent interactions inherent to the strong SOC. , Also, several efforts have been made to find other candidate materials; along this direction, materials exploration is extended to the systems containing 4f rare-earth (RE) ions. , Compared to the 4d/5d-based Mott insulators, the 4f electron systems can also exhibit the Kitaev-type interactions stabilized by strong SOC and dedicate exchange pathways in the edge-sharing honeycomb network, − but that is less experimentally studied for investigating the Kitaev quantum spin liquid physics. Another difference is that the exchange interactions between RE 3+ local moments are relatively small, which let us safely consider the dominance of nearest-neighbor spin interactions and easily realize the field-tuned QSL phase at a low field accessible in the laboratory. − Very recently, several studies have been conducted on the RE-based Kitaev candidates with different 4f electron configurations including trichlorides YbX 3 (X = F, Cl, Br, and I), − A 2 REO 3 (A = Li and Na; RE = Pr and Tb) , and RE 2 Si 2 O 7 (RE = Er–Yb) oxides, − and chalcohalides REChX (Ch = O, S, Se, and Te, X = F, Cl, Br, I). , Unfortunately, the experimental identification on Kitaev QSL states remains to be challenging since most discovered RE-based Kitaev materials form a magnetic ordered phase at low temperatures. For example, the relatively well-studied YbCl 3 exhibits a short-range magnetic order below 1.20 K and long-range AFM order with a Néel temperature T N of ∼0.60 K, and Na 2 PrO 3 enters into the AFM state below a T N of ∼4.6 K .…”

On the Crystal Chemistry of RE2Si2O7: Revisited Structures, Group–Subgroup Relationship, and Insights of Ce3+-Activated Radioluminescence

“…Unfortunately, the structures of the orthorhombic E­(δ)-type (Eu–Ho and Y) and the triclinic F-type (Sm and Eu) RE 2 Si 2 O 7 remain controversial hitherto. The controversy of the E­(δ) phase lies in the fact that which space group, i.e., Pna 2 1 (Eu–Ho) or Pnma (Y), is more accurate to describe the orthorhombic structure. − In essence, the noncentrosymmetric (polar) Pna 2 1 is the maximal translationengleiche subgroup of the centrosymmetric (nonpolar) Pnma , the most frequent space group (∼7.5%) in the Inorganic Crystal Structure Database (ICSD). According to Friedel’s law, members of a Friedel pair, say hkl and , have equal amplitude if the anomalous scattering is neglected.…”

Néel ordering in the distorted honeycomb pyrosilicate: C–Er2Si2O7

“…Lu 2 Si 2 O 7 and Y 2 Si 2 O 7 are nonmagnetic, so they may provide a useful non-magnetic analog to C-Er 2 Si 2 O 7 . Meanwhile, the magnetism of Tm 2 Si 2 O 7 has not been thoroughly investigated, though it does show a lowtemperature Schottky-like anomaly in the specific heat [23], similar to Yb 2 Si 2 O 7 . Yb 2 Si 2 O 7 does not magnetically order down to 50 mK in zero field, and exhibits a field-induced phase similar to the triplon Bose-Einstein condensates observed in 3d transition metal based dimer magnets.…”