Crystal growth and characterization of the pyrochlore Tb₂Ti₂O₇

Abstract

Terbium titanate (Tb 2 Ti 2 O 7 ) is a spin-ice material with remarkable magneto-optical properties. It has a high Verdet constant and is a promising substrate crystal for the epitaxy of quantum materials with the pyrochlore structure. Large single crystals with adequate quality of Tb 2 Ti 2 O 7 or any pyrochlore are not available so far. Here we report the growth of high-quality bulk crystals using the Czochralski method to pull crystals from the melt. Prior work using the automated Czochralski method has suffered from growth instabilities like diameter fluctuation, foot formation and subsequent spiraling shortly after the seeding stage. In this study, the volumes of the crystals were strongly increased to several cubic centimeters by means of manual growth control, leading to crystal diameters up to 40 mm and crystal lengths up to 10 mm. Rocking curve measurements revealed full width at half maximum values between 28 and 40 ′′ for 222 reflections. The specific heat capacity c p was measured between room temperature and 1573 K by dynamic differential scanning calorimetry and shows the typical slow parabolic rise. In contrast, the thermal conductivity κ(T ) shows a minimum near 700 K and increases at higher temperature T . Optical spectroscopy was performed at room temperature from the ultraviolet to the near infrared region, and additionally in the near infrared region up to 1623 K. The optical transmission properties and the crystal color are interpreted to be influenced by partial oxidation of Tb 3+ to Tb 4+ .

Czochralski growth and characterization of TbxGd1−xScO3and TbxDy1−xScO3solid-solution single crystals

“…Apparently, the 1/T law is insufficient to describe thermal conductivity of the studied compounds, because the increase of at elevated temperatures cannot be explained by that model. Recently, an analogous behavior of the thermal conductivity could be observed for the inverse spinel MgGa2O4 22 as well as the pyrochlore Tb2Ti2O7 23 . For the spinel it was suggested, that cations exchanging their site at elevated temperatures contribute to thermal transport.…”

“…An empirical formula with a linear term added to equation (3) can describe λ(T) well (see equation (4)). Here the first inverse term describes the heat transport by phonons, while the second linear term might be related to transportation of thermal energy by any type of carriers 23 . At least for the REScO3 a significant portion (ca.…”

Thermal conductivity of rare-earth scandates in comparison to other oxidic substrate crystals

“…Recently, an analogous increase of the thermal conductivity could be observed for the inverse spinel MgGa 2 O 4 [46] as well as the pyrochlore Tb 2 Ti 2 O 7 [47]. For the spinel it was suggested, that cations exchanging their site at elevated temperatures contribute to thermal transport.…”

“…An empirical formula with a linear term added to equation ( 5) can describe λ(T ) well (see equation ( 6)). Here the first inverse term describes the heat transport by phonons, while the second linear term might be related to transportation of thermal energy by any type of charge carriers [47]. For electrically conducting materials, free electrons could contribute to heat transport [48].…”

A review on magneto-optical ceramics for Faraday isolators

“…TGG crystals are widely discussed and applied in these years as they possess high Verdet constant ( -136 rad•T -1 •m -1 at 633 nm, -38 rad•T -1 •m -1 at 1064 nm), wide transparent band (500-1500 nm), and high thermal conductivity (4.5 W•m -1 •K -1 ) [2,14,49,52,63,64]. Though MO crystals have occupied major markets, the fabrication of MO crystals is facing many problems [65][66][67][68][69][70][71][72][73][74], including component volatilization, incongruent melting, high melting point, phase transition, time-consuming, size limitation, cracking, and so on.…”