Developments in Ceramic Materials Research

Synthesis, Spectroscopic and Magnetic Studies… 107
attributed to the exchange interactions between the Ti(III) ions in the pure compound. The
resonance shown in Figure 4(a) is the result of the collapse due to the exchange of those
expected for the three different Ti(III) ions.
The ESR result in the Sc(III) compound doped with Ti(III) may be qualitatively
understood considering the theory described by Abragam and Blaney [35]. The D ground
state orbital of Ti(III) is broken by the cubic field of the octahedron of oxygen ligands in a
ground state triplet (Γ5) and an excited state doublet (Γ3), the splitting being Δ= 10 Dq ≅
17300 cm -1 , according to our spectroscopic data. A distortion of the octahedron having
trigonal symmetry breaks the orbital degeneracy of the (Γ5) triplet into a singlet and a doublet
with an energy splitting δ. The spin orbit interactions λLS (λ= 145 cm -1 for the TI(III) ion)
mixes these states and gives rise to g-values depending on the crystalline field splitting Δ and
δ and on λ. The range of observed g-values indicates that the singlet orbital state is lowest in
energy. Neglecting mixture of the group stated spin doublet with excited states at Δ ≅ 17300
cm -1 due to the spin-orbital interactions, the g-factor were obtained from Ref. [35].
The presence of three Ti(III) sites introduces a large uncertainty in the g-factors
calculated from the data. However, using the free ion spin-orbit parameter λ for Ti(III), the
observed g-values indicate δ≅ 1000 cm -1 for the average trigonal splitting. In the Ti(III) doped
sample, the resonance narrow and move to lower fields with increasing temperature [Figure
(4b)]. This fact results as a consequence of a dynamic Jahn-Teller averaging of the signal that
occurs above 50 K. The same process would be responsible for the last relaxation mechanism
which vanishes at T> 100 K. These results are similar to those observed in single crystal
samples of Chrysoberyl [36] and LaMgAl11O19 [37] two material investigated for their
potential applications for tunable lasers, in which the Ti(III) ions occupy similar octahedral
sites with oxygen ligands.
5.2. ESR of V(PO3)3
The X-band ESR spectrum of V(PO3)3 recordered at 4.2 K shows only a weak signal
belonging to the V(III) ions at a magnetic field of about 1580 Gauss. This observed “halffield”
signal corresponds to the forbidden ΔMs= ±2 transition [16]. The zero field splitting
parameter D was estimated as between 2 and 8 cm -1 , which is in the range usually found for
V(III) compounds [16,38].
5.3. ESR of M(PO3)3 (M= Mo and Cr) and Cr2(P6O18)
The ESR spectra of these compounds at 4.2 K are given in Figure 5. For the Mo(PO3)3
phase no signal was observed at temperatures higher than 120 K. Therefore, we can attributed
the signal observed at low temperatures to Mo(III) ions present in the compound and enable
us to exclude the existence of Mo(V) impurities [39,40]. The spectrum can only been
explained by considering the presence of more than one different environment for
molibdenum (Figure 5). Assuming that the g tensor is isotropic, as usually occurs for Mo(III)
compounds. An average g value of 1.89 can be deduced. The intensity of the signal was so
weak that the spectrum at Q-band cannot be recordered. In the case of the chromium phase,