Abstract: Vitreous solid compositions of formula I:Te.sub.w Se.sub.y X.sub.x Z.sub.z (I)whereinX represents at least one halogen selected from chlorine, bromine and iodine,Z represents at least one element selected from As, Sb and Bi,w, x, y and z represent the molar percentages respectively of elements Te, X, Se and Z,w being a number varying from 5 to 50,x being a number varying from 5 to x.sub.1,y being a number varying from 5 to 80,z being a number varying from 5 to z.sub.1,the numbers w, x, y and z being such that the sum (w+x+y+z) is equal to 100,the numbers x.sub.1 and z.sub.1 being such that:when X represents mostly iodine, x.sub.1 =50 and z.sub.1 =60,when X represents mostly bromine, x.sub.1 =60 and z.sub.1 =50, andwhen X represents mostly chlorine, x.sub.1 =60 and z.sub.

Abstract: A solid vitreous composition has the formula: Te.sub.100-x-z X.sub.x Z.sub.z wherein x represents chlorine, bromine or iodine, Z represents sulfur and/or selenium; x represents the molar percentage of X and ranges from 5 to 67; z represents the molar percentage of Z and ranged from 0 to 60; it being understood that the sum (x+z) ranges from 33 to 85. A method for the preparation of this composition is disclosed as is its use in the field of optoelectronics and infra-red transmission.