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

• Published in: Crystal growth & design Vol. 20; no. 10; pp. 6636 - 6648
• Main Authors: Ciomaga Hatnean, Monica, Petrenko, Oleg A, Lees, Martin R, Orton, Tom E, Balakrishnan, Geetha
• Format: Journal Article
• Language: English
• Published: American Chemical Society 07.10.2020
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.0c00792

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, R2Si2O7 (with R = Er, Ho, and Tm). Through a systematic study, we have optimized the growth conditions for Er2Si2O7. We have grown, for the first time using the floating zone method, crystal boules of Ho2Si2O7 and Tm2Si2O7 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 rare-earth silicate compounds in the temperature–composition phase diagrams of the R-Si-O systems. The addition of a small amount of SiO2 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 R2Si2O7 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 Er2Si2O7 and a Schottky anomaly centered around 3.5 K in C-type Tm2Si2O7, with an upturn in C(T)/T below 1 K suggesting the onset of short-range magnetic correlations. Magnetic susceptibility data of E-type Ho2Si2O7 reveals an antiferromagnetic ordering of the Ho spins below T N = 2.3 K.