The elpasolite type crystals areintensively studiedby various methods /I to 3/. In particular Cs2NaYC16 crystals contrary to numerous representatives of the series do not undergo a low-temperature phase transition. However, small distortions of crystal structure have been observed by means of ligand Ce ENDOR on 23Na nuclei /4/. In 1 5 1 it was shown that the crystal field symmetry remains the cubic one under Gd3+ admixture and the splitting of the 23Na ENDOR spectrum lines may be attributed to the nuclear quadrupole interaction.Ligand nuclear quadrupole interaction is known to be the consequence of the electric field gradient on the nucleus. The value of the interaction must correlate with the physical parameters of the admixture of rare-earth paramagnetic ions. The ligand ENDOR of Ce3+ and Gd3+ ions being studied recently, in the present note we report the Yb3+ ion ligand interaction in order to solve unambiguously the problem of the nature of the splitting of the 23Na ENDOR spectrum lines.
3+Cs2NaYC16 single crystals were grown from the charge of the corresponding composition of Cs, Na, and Y dehydrated halogenides according to the Bridgman method. The concentration of Yb3+ ions substituting Y3+ ions was 0.005 to 0.05%. The crystals had no faces. To carry out the ENDOR measurements the crystals were oriented on the X-ray diffractometer.The EPR spectrum of Yb3+ even isotopes at T = 4 K is a single line with isotropic g = -2.584(1) /6/ evidencing the cubic symmetry of the admixture centre. Two "lYb (I = 1/2) and 173Yb (I = 5/2) isotopes with hyperfine structure constants with different sign, 171A = -0.0577(1) T and 173A = 0.0157(1) T, have been observed in the Yb3+ ion EPR spectrum. The absolute sign of the 1) Sibirskii Trakt 10/7, 420029 Kazan, USSR.
