Glasses Technology

Glasse Parent Description

Glasses of the BaO — Nb.sub.2 O.sub.5 — GeO.sub.2, SrO — Nb.sub.2 O.sub.5 — GeO.sub.2 and PbO — Nb.sub.2 O.sub.5 — GeO.sub.2 system in selected proportions have been found to have desirable properties from the standpoint of transparency and stability and are useful for a wide variety of purposes. Of particular interest is the finding that these glasses can be heat treated to produce transparent glass-ceramics having an index of refraction higher than that of the glass and which specifically may be in excess of 2.000. The glass-ceramics which are capable of being formed from glasses within the above-described glass system have high dielectric constants; e.g. in excess of 50 and low dissipation factors; e.g. about 3.5% or less. Both transparent and non-transparent or opaque glass-ceramics may be obtained in accordance with this invention possessing the aforementioned desirable properties.

Because they have been found to have excellent dielectric properties, including high dielectric constants and very low dielectric losses, the glass-ceramics produced in accordance with the present invention are suitable for use in a variety of electrical devices, such as capacitors, electroluminescent cells, wave guides, thick-film dielectric pastes for microelectronic printed circuits and the like.

Thermally crystallizable glasses of the above-specified systems can, during an appropriate heat treatment process, be converted to a transparent, inorganic crystalline oxide ceramic material having any desired dielectric constant between a selected upper and lower limit. The ceramic material thus formed, also known as a glass-ceramic, contains a major portion of very tiny crystals embedded in a minor glassy matrix remaining as a result of the thermal crystallization.

Glass-ceramics of the present invention can also be prepared in the form of small chips, of a size of about one-fourth inch or less, which are suitable for use as support carriers for electronic microcircuits. Chip capacitors are produced by casting, pressing and metallizing/heat treating in a continuous operation. Such capacitors are of the general purposes or high-frequency/positive temperature coefficient. Dielectric constants are in the range of 50 or more and the dissipation factor is preferably less than 3.5% and usually less than 1% with the temperature coefficient of capacitance being positive or negative.

The following compositions were prepared.*

*In forming the glass melts of the compositions, the batch materials consisted of GeO.sub.2, Nb.sub.2 O.sub.5 and PbO, charged as the oxides, while SrO and BaO were charged as strontium carbonate and barium carbonate, respectively.

The foregoing Tables show that there exists an interrelationship between proportions of ingredients and molar ratios. Illustratively, composition 1 with 14.3 mole percent SrO, which is outside the claimed range fails to form a glass. The BaO containing compositions parallel the SrO compositions. For example, sample 3 with 14.3 mole percent BaO also failed to form a glass. Also, compositions 6 and 7 wherein the ratio of Nb.sub.2 O.sub.5 : RO is outside the range, could not be formed into transparent or opaque glass-ceramics. Composition 9, which is just outside the claimed upper limit for BaO content could only be formed into an opaque glass-ceramic.

For the lead oxide containing compositions it developed that the behavioral characteristics were quite different from the RO containing composition. For instance, composition 5, similar in ratios and proportions to composition 6 (BaO) and 7 (SrO) could be heat treated to form a transparent glass-ceramic having good electrical properties whereas compositions 6 and 7 did not form a glass-ceramic.

Also, compositions 14 and 15, which fell inside the compositional limitations, but outside the molar proportion limitations did not form transparent glass-ceramics.

While the glasses and glass-ceramics of the invention have been discussed in terms of the sole essential ingredients, it will be evident to those skilled in the art that minor amounts, preferably not more that 10% and most preferably no more than 5% by weight of other metal oxides which are compatible with the glass and glass-ceramic compositions can be used. Care should be taken, however, to insure that such other metal oxides do not materially affect the basic characteristics of the glasses and glass-ceramics of the present invention, including the high dielectric constants and dissipation factors and high indices of refraction.