O objetivo deste trabalho foi o estudo do íon Fe3+ em monocristais e fibras monocristalinas de LiNbO3, através da técnica espectroscópica da Ressonância Paramagnética Eletrônica (RPE), nas freqüências de 10 e 34GHz, à temperatura ambiente. O Hamiltoniano de Spin para o íon Fe3+ ocupando um sítio de simetria trigonal (C3v) é dado por: H = 'beta' 'VET.H' 'VET.g' 'VET.S' + 'B20O20+B40O40 . Foram analisadas três amostras de LiNbO3, com diferentes concentrações de Fe3+ e os parâmetros de campo cristalino e fator-g encontrados são: fibra (0.3 mol% de Fe3+) g = 1.9908 '+OU-' 0.0002, 'B. SUP. 0 INF. 2' = 5.4'+OU-'0.2x10-2 cm-1 , 'B. SUP. 0 INF. 4' = -7.7'+OU-'1.5x10-5cm-1, monocristal 90 (0.22 mol%) g = 2.0043'+OU-'0.0002, 'B. SUP. 0 INF. 2' = 5.35'+OU-'0.25x10-2 cm-1, 'B. SUP. 0 INF. 4'= - 4.03'+OU-'1.4x10-5cm-1, monocristal 99 (0.02 mol%) g = 2.0026'+OU-'0.0004, 'B. SUP. 0 INF. 2' = 5.4'+OU-'0.3x10-2 cm-1, 'B. SUP. 0 INF. 4' = - 8.33'+OU-'1.6x10-5cm-1. Foi medida e analisada a dependência angular da largura das linhas nas duas bandas de freqüências. Através de modelos teóricos (Watanabe, Orbach-Das-Sharma, Spinspin, Spin-spin Spin-órbita) calculamos o parâmetro de desdobramento a campo zero, 'B. SUP. 0 INF. 2', do estado fundamental do íon Fe3+, para determinar qual o sítio que este íon ocupa no LiNbO3.

We report EPR measurements of Fe3+ ion in bulk LiNbO3 single crystals and in the form of fibers. Spin Hamiltonian for the Fe3+ ion in a trigonal symmetry (C3v) site is given by: H = 'beta' 'VET.H' 'VET.g' 'VET.S' + 'B20O20+B40O40. Measurements were performed at room temperature and two frequency bands, 10 and 34GHz, using three samples of LiNbO3 with different concentrations of Fe3+ g-factor and the crystal field parameters were found to be: for fiber (0.3 mol% of Fe3+) g = 1.9908 '+OU-' 0.0002, 'B. SUP. 0 INF. 2' = 5.4'+OU-'0.2x10-2 cm-1 , 'B. SUP. 0 INF. 4' = -7.7'+OU-'1.5x10-5cm-1, for the single crystal 90 (0.22 mol%) g = 2.0043'+OU-'0.0002, 'B. SUP. 0 INF. 2' = 5.35'+OU '0.25x10-2 cm-1, 'B. SUP. 0 INF. 4'= - 4.03'+OU-'1.4x10-5 cm-1, and for the single crystal 99 (0.02 mol%) g = 2.0026'+OU-'0.0004, 'B. SUP. 0 INF. 2' = 5.4'+OU-'0.3x10-2 cm-1, 'B. SUP. 0 INF. 4' = - 8.33'+OU-'1.6x10-5cm-1. The angular dependence of the line width were also measured and compared with theoretical model. To determine the substitutional site of Fe3+ ion in the LiNbO3 lattice, we calculated the zero field splitting parameter 'B. SUP. 0 INF. 2' of the ground state, using many theoretical models (Watanabe, Orbach-Das-Sharma, Spin-spin, Spin-Spin Spinorbita).