亚碲酸铋Bi_2TeO_5单晶的化学计量比的研究

Investigation of the Stoichiometry of Bismuth Tellurite Bi_2TeO_5 Single Crystals

Bismuth tellurite Bi 2TeO 5 is a novel nonlinear crystal with interesting physical properties.The crystal structure belongs to the mm 2 symmetry and can be described as 2 3 1 fluorite type superstructure,derived from a hypothetically ordered totally oxidized Bi 2TeO 6 structure.The lattice contains 17% open oxygen positions and cation coordination sites between 5 and 8.The material,therefore is an excellent host for several dopants with segregation coefficients close to unity.The most interesting feature of the crystal is a long living(years)photorefractive signal that developed in the four wave mixing process without specific fixing.This feature enables the application of the crystal as hologram recording material. Single crystals of Bi 2TeO 5 can be grown by the Czochralski method.One of the key problem of the growth process is the control of the stoichiometry of the crystals.The high vapor pressure of TeO 2 at the melting point results in the nonstoichiometric evaporation of the melt and by altering the initial Bi 2O 3/TeO 2 creates continuously shifted melt composition.Between 550℃ and 700℃ the oxidation state of Bi 2TeO 5 may be modified,since the fully oxidized Bi 2TeO 6 compound is thermodynamically stable in this range.Crystals grown from the melt at 906℃,depending on the post growth period(annealing and cooling down processes)might be partly or fully oxidized.

Bismuth tellurite Bi 2TeO 5 is a novel nonlinear crystal with interesting physical properties.The crystal structure belongs to the mm 2 symmetry and can be described as 2 3 1 fluorite type superstructure,derived from a hypothetically ordered totally oxidized Bi 2TeO 6 structure.The lattice contains 17% open oxygen positions and cation coordination sites between 5 and 8.The material,therefore is an excellent host for several dopants with segregation coefficients close to unity.The most interesting f...