Effect of oxide additions on the polymorphism of tantalum pentoxide. II. ""Stabilization"" of the high temperature structure type

Abstract

The hi gh temperature, ap paren tl y tetragonal, polymorph of ta ntalum pentoxide ca n be ob tai ned at room tempe rature by quen c hin g a specim en co ntainin g 2-5 mole perce nt of the follow in g oxides: S n0 2' Ga,O", C r,O ", Fe 20 ", Sc20", or MgO. All the x·ray pattern s ca n be ind exed on a body ce ntered tetrago nal cell with a = 3.830 A, C = 35.68 A· However, P ,O " V 20 5 , N b20 " ZrO " LU 20 3, NiO , or ZnO do not stabilize the tetragonal form at room te mperature. Sin gle crystals of scand ium "stab ilized " Ta20 , have bee n grow n by th e Czochra ls ki tec hnique.Key word s: High temperature polymorp h; s in gle crystals; sta biliza tion; ta ntalum ox id e.

Characterization and sintering of a porous glass-ceramic in the system Na2O-B2O3-Ta2O5

“…Small peaks were identified as consistent with a low temperature orthorhombic form of Ta20 5. This finding is in agreement with Roth et al [12] who describe this form as stable up to 1360 ~ The presence of a second minor phase possible Na2TasO2~ can, however, not be excluded.…”

“…The major phases are Ta20 5 and orthorhombic Na2TasOzx. After the first two steps (1100 and 1250 ~ sintering temperatures) Ta205 is present in its orthorhombic low temperature form, which is in agreement with Roth et al and Waring et al [12,13] as well as with Reisman et al [14] and Terao's [15] findings. The temperature related polymorphism of Ta20 5 is well known and has been extensively studied.…”

Effect of oxide additions on the polymorphism of tantalum pentoxide. III. ""Stabilization"" of the low temperature structure type

“…These other oxides were Mo0 3 , W0 3 , Si0 2 , Ge0 2, B 2 0 3 , and AI20 : l • Some of the results previously reported for Zr0 2 [5] are duplicated here for discussion. The specimen preparation and test methods were the same as reported in the previous paper [5].…”

“…[5]) as this is the only system yet found in which the "C"-line is displaced (from pure Tat 05) toward higher 2(} (smaller d). It can be assumed that HfOz will also cause this type of displacement.…”

“…The low-te mperature form of Ta20 5 has an, as yet, unknown stru c ture related to th e low-tem perature form of Nb z0 5 as well as to 0'-U3 0 8 a nd 0'-U03• As TaZ0 5 exhibits a reversible phase transition a t about 1360°C to a struc turally dissimilar high-te mperature form [lP it is not possible to grow sin gle crys tals of the roo m temperature stable form by conve ntion al high-temperature techniques s uc h as the Verneuil and the Czochralski me thods . Whereas impurities appear to e nter into solid solution in the high-te mperature form of Ta205 [2] the y a ppare ntly form ne w discrete phases in the low-te mperature form [2].…”