S C

IE N

T IF

IC H

IG H

LI G

H T

S M

A T

T E

R A

T E

X T

R E

M E

S

3 1 I H I G H L I G H T S 2 0 2 1

Although lanthanum and yttrium are similar, their hydrides are different: YH6 and LaH10 do exist, whereas LaH6 and YH10 do not. The research showed that both structures can be stabilised by adding the other element. For example, the stability of LaH6 can be improved by adding 30 percent of yttrium, and the critical temperature of superconductivity of the resulting compound is higher than that of YH6. It is also possible to stabilise mixed (La,Y)H10 decahydrides with different yttrium content.

The study also helped to elucidate the general profile of superconductivity in ternary hydrides. It was found

that ternary and quaternary hydrides have progressively less ordered structures and a much greater width of the superconducting transition than binary hydrides. To produce ternary hydrides, longer and more intensive laser heating is required compared with their binary counterparts. An important observation was that the critical temperature of superconductivity of the resulting ternary (La,Y)H10 hydrides remains very stable (~240 250 K) despite wide variations of yttrium concentration. Clearly, studies of ternary hydrides hold much promise for stabilising unstable compounds and enhancing their superconducting performance.

PRINCIPAL PUBLICATION AND AUTHORS

Superconductivity at 253 K in lanthanum yttrium ternary hydrides, D.V. Semenok (a), I.A. Troyan (b), A.G. Ivanova (b), A.G. Kvashnin (a), I.A. Kruglov (c,d), M. Hanfland (e), A.V. Sadakov (f), O.A. Sobolevskiy (f), K.S. Pervakov (f), I.S. Lyubutin (b), K.V. Glazyrin (g), N. Giordano (g), D.N. Karimov (b), A.L. Vasiliev (b,d), R. Akashi (h), V.M. Pudalov (f,i) A.R. Oganov (a),, Mater. Today 48, 18-28 (2021); https:/doi.org/10.1016/j.mattod.2021.03.025 (a) Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, Moscow (Russia) (b) Shubnikov Institute of Crystallography, Federal Scientific Research Center Crystallography and Photonics, Russian Academy of Sciences, Moscow (Russia) (c) Dukhov Research Institute of Automatics (VNIIA), Moscow (Russia) (d) Moscow Institute of Physics and Technology, Dolgoprudny (Russia) (e) ESRF (f) P.N. Lebedev Physical Institute, Russian Academy of Sciences, Moscow (Russia) (g) Deutsches Elektronen-Synchrotron, Hamburg (Germany) (h) University of Tokyo, Tokyo (Japan) (i) National Research University Higher School of Economics, Moscow (Russia)

REFERENCES

[1] A.P. Drozdov et al., Nature 525, 73 (2015). [2] A.P. Drozdov et al., Nature 569, 528 (2019). [3] D.V. Semenok et al., Mater. Today 33, 36 (2019). [4] I.A. Troyan et al., Adv. Mater. 33, 2006832 (2021). [5] E. Snider et al., Nature 586, 373 (2020).

Fig. 18: Left: Experimental X-ray diffraction patterns and Le Bail refinements of the crystal unit cell parameters of Fm3m-(La,Y)H10 (DAC SL1). The experimental data, fit and residues are shown by red, black and green lines, respectively. Right: Fragment of crystal structure of (La,Y)H10 where Y and La are neighbours (for illustrative purposes).