Local structure of titanium pair centers in SrF2 crystals: EPR and ENDOR spectroscopic studies

Electron spin relaxation of exchange coupled pairs of transition metal ions in solids. pairs and single ions in crystals

“…Single crystals of BaF 2 were grown in gaseous helium-fluorine atmosphere by the Bridgman technique as it was described earlier [8,10]. Titanium was introduced into a melt as TiF 4 compound in conditions of fluorine excess.…”

“…Ti 2þ -Ti 2þ ðS ¼ 2Þ pairs in SrF 2 were identified by their characteristic quartet of lines in the multiline EPR spectrum at low temperatures and their temperature dependence showed that the pairs are ferrromagnetically coupled [18]. In ENDOR studies of the pair in SrF 2 an unusual behavior of fluorine atoms surrounding the Ti 2þ -Ti 2þ pairs was discovered [10]. An analysis of angular dependence of the 19 F frequencies in the first, second and third coordination spheres showed that one of the fluorine planes surrounded Ti 2þ is 45°rotated with respect to the host lattice.…”

“…Moreover, Cu 2þ -Cu 2þ pairs were observed in BaF 2 [8], Ti 2þ -Ti 2þ pairs in CaF 2 [9] and in SrF 2 [9,10], and Yb 3þ -Yb 3þ pairs were found in SrF 2 [11]. The electron spin relaxation of exchange coupled pairs was studied for Cu 2þ -Cu 2þ in zinc(II)bis(diethyldithiocarbamate) [12], for Cr 3þ -Cr 3þ in Al 2 O 3 [13], and for Ir 3þ -Ir 3þ in ðNH 4 Þ 2 PtCl 6 [14].…”

“…Ti 2þ ion ð3d 2 ; S ¼ 1Þ in the cubic environment has orbitally non-degenerate ground state, thus it is not the Jahn-Teller active ion and off-center shift is not expected. In fact, EPR spectra of Ti 2þ in SrF 2 [10,18], CaF 2 [9] and SrCl 2 [19] consist of a single resonance line indicating the cubic crystal field symmetry at Ti 2þ located in the center of the ½TiF 8 cube. The orbital ground state of Ti 2þ in a cube of O h symmetry is an orbital singlet 3 A 2 with the lowest excited state 3 T 2 of D ¼ 6900 cm À1 [20].…”

“…The orbital ground state of Ti 2þ in a cube of O h symmetry is an orbital singlet 3 A 2 with the lowest excited state 3 T 2 of D ¼ 6900 cm À1 [20]. The EPR line is described by the isotropic g-factor g ¼ 2:0023 À 8k=D ¼ 1:933 [10,18] where k ¼ þ60 cm À1 is the spin-orbit coupling constant. This line is produced by non-magnetic isotope 48 Ti having abundance of 73.72%.…”