Europium(II) titanate explained

Europium(II) titanate is a black mixed oxide of europium and titanium, with the chemical formula of EuTiO₃. It crystallizes in the perovskite structure.^[1]

History

EuTiO₃ was first examined in 1966 by McGuire, Shafer, Joenk, Halperin and Pickart where the magnetic structure was examined.^[2] This compound received more attention at the beginning of the 21st century (2001 to 2015) due to the low-temperature phase transition to antiferromagnetic behavior at T_N = 5.5 K, which has a significant influence on the dielectric constant.^{[3] [4]}

Preparation

Dried Eu₂O₃ and Ti₂O₃ are mixed 1:1 and reacted in an argon atmosphere at 1400 °C:^[5]

Eu2O3 + Ti2O3 -> 2EuTiO3

The europium is reduced and the titanium is oxidized.

Properties

Europium(II) titanate has two different crystal forms depending on the temperature. The phase transition occurs at 282 K.^[6] The low temperature form crystallizes in the tetragonal space group I4/mcm (space group No. 140) with the lattice parameters a = 551.92(2) pm, c = 781.64(8) pm (measured at 90 K). The higher temperature form has a cubic form with Pmm (space group No. 221) with lattice parameter a = 390.82(2) pm (measured at 300 K).^[7] The transition temperature of the crystal structure from the low-temperature to the high-temperature phase increases with increasing pressure.^[8] The compound becomes G-type antiferromagnetic below 5.5 K.^[9] The specific heat capacity is 125 J·mol⁻¹·K⁻¹ (at 600 K). 125 J·mol⁻¹·K⁻¹290 K is 7,6 W·m⁻¹·K⁻¹ and the electrical conductivity is 10⁵ (Ω·m)⁻¹(at 330 K).

Notes and References

1. 1. Muta, Hiroaki . Thermoelectric Properties of Lanthanum-Doped Europium Titanate . Materials Transactions . 7 . 2005 . 46 . 1466–1469 . 10.2320/matertrans.46.1466. free .
2. T. R. McGuire, M. W. Shafer, R. J. Joenk, H. A. Halperin, and S. J. Pickart . Magnetic structure of EuTiO₃ . Journal of Applied Physics . 1966 . 37 . 3 . 981. 10.1063/1.1708549 . 1966JAP....37..981M .
3. S. Kamba, D. Nuzhnyy, P. Vaněk, M. Savinov, K. Knížek, Z. Shen, E. Šantavá, K. Maca, M. Sadowski, J. Petzelt . Magnetodielectric effect and optic soft mode behaviour in quantum paraelectric EuTiO₃ ceramics . Europhysics Letters . 2007 . 80 . 2 . 27002 . 10.1209/0295-5075/80/27002. 0706.1882 . 2007EL.....8027002K . 13856279 .
4. . Coupling between magnetism and dielectric properties in quantum paraelectric EuTiO₃ . Physical Review B . 2001 . 64 . 5 . 054415-1–054415-4. 10.1103/PhysRevB.64.054415 . 2001PhRvB..64e4415K .
5. J. Köhler, R. Dinnebier, A. Bussmann-Holder . Structural instability of EuTiO₃ from X-ray powder diffraction . Phase Transitions . 11 . 2012 . 85 . 949–955 . 1205.5374 . 10.1080/01411594.2012.709634. 2012PhaTr..85..949K . 94709465 .
6. Bussmann-Holder, J. Köhler, R. K. Kremer, J. M. Law . Relation between structural instabilities in EuTiO3 and SrTiO₃ . Physical Review B . 2011 . 83 . 21 . 212102 . 10.1103/PhysRevB.83.212102. 1105.6029 . 2011PhRvB..83u2102B . 118638434 .
7. A. Bussmann-Holder, Z. Guguchia, J. Köhler, H. Keller, A. Shengelaya, A. R. Bishop . Hybrid paramagnon phonon modes at elevated temperatures in EuTiO₃ . New Journal of Physics . 2012 . 14 . 9 . 093013 . 10.1088/1367-2630/14/9/093013. 1205.6287 . 2012NJPh...14i3013B . 118479381 .
8. P. Parisiades, E. Liarokapis, J. Köhler, A. Bussmann-Holder, M. Mezouar . Pressure-temperature phase diagram of multiferroic EuTiO₃ . Physical Review B . 2015 . 92 . 6 . 064102 . 10.1103/PhysRevB.92.064102. 1505.05049 . 2015PhRvB..92f4102P . 118250289 .
9. Z. Guguchia, H. Keller, A. Bussmann-Holder, J. Köhler, R. K. Kremer . The low temperature magnetic phase diagram of Eu_xSr_1−xTiO₃ . European Physical Journal B . 2013 . 86 . 10 . 409–412 . 10.1140/epjb/e2013-40632-y. 2013EPJB...86..409G . 123512501 .