Transparent ceramics

Abstract

A transparent, complex oxide ceramic having the formula:(Sr.sub.1-x Me'.sub.x) (Li.sub.1/4 Me".sub.3/4) O.sub.3wherein x is 0.01-0.50, Me' is at least one metal selected from the group of Ca, Ba, and Pb, and Me" is Nb and/or Ta. The present ceramics can be used in the fabrication of gas discharge tubes and for infrared-ray tubes as optical devices and as substrates for higher quality electronic parts, and as an insulator for microwave frequency electronic devices.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to poreless ceramics which have excellent optical transmission properties.

Description of the Prior Art

Generally, poreless ceramics have excellent thermal, electrical, chemical and optical properties. Transparent ceramic materials can be used in the fabrication of, for example, crystron tubes, power tubes, antenna windows, integral circuit substrates, high pressure gas-discharge tubes, rocket nozzles, and the like. Currently, many transparent ceramic materials such as Al.sub.2 O.sub.3, MgO, Y.sub.2 O.sub.3, BeO, Gd.sub.2 O.sub.3, LiAl.sub.5 O.sub.8, CaO, ThO.sub.2, MgAl.sub.2 O.sub.5, (Pb,La) (Ti,Zr)O.sub.3 and the like, are known. However, the conventional transparent ceramic materials all have problems concerning their dielectric constants and thermal constants. In addition, the conventional ceramic materials have to be fabricated under hot pressing conditions or special sintering atmospheres and at high sintering temperatures of about 2000.degree. C. Therefore, the cost of these materials becomes expensive because of the necessity of indispensible, complicated facilities and because of difficulties in manufacturing.

A need, therefore, continues to exist for a ceramic material which is inexpensive to prepare and which possesses good optical transmission characteristics and dielectric properties.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide poreless ceramics having good optical transmission characteristics over a wide wavelength range and excellent dielectric properties.

Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a transparent, complex oxide ceramic having the formula:

(Sr.sub.1-x Me'.sub.x)(Li.sub.1/4 Me".sub.3/4)O.sub.3 wherein Me' is at least one element selected from the group of Ca, Ba, and Pb; Me" is Nb and/or Ta and x is 0.01 to 0.50.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The oxide compound of the present invention is a transparent binary oxide of the perovskite-type having the formula:

Sr(Li.sub.1/4 Me".sub.3/4)O.sub.3 - Me'(Li.sub.1/4 Me".sub.3/4)O.sub.3 wherein Me' is at least one element selected from the group of Ba, Ca and Pb, and Me" is Ta and/or Nb. This composition can be prepared from mixtures of raw materials by conventional ceramic fabrication techniques.

The transparent ceramic materials of this invention may be prepared in the following manner. The raw materials such as SrO, BaO, CaO, PbO, Li.sub.2 O, Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5 are accurately weighed out in prescribed amounts, are mixed in a ball mill and calcined at 900.degree.-1100.degree. C.

It is most desirable that the raw materials be of high purity. Suitable raw materials include such metal compounds as the hydroxides, carbonates and oxalates all of which can be converted to the corresponding oxide upon heating. The calcined powder is then pulverized. The powder thus obtained is mixed with a binder, such as water or polyvinyl alcohol, and the mixture is shaped under a pressure of about 0.5-2 tons/cm.sup.2 into, for example, a plate having a diameter of 20 mm and a thickness of 1 mm. The plates are then sintered under temperature conditions of 1150.degree.-1450.degree. C. over a period of 2-4 hours, preferably under an oxygen atmosphere.

The composition of the present transparent ceramic material is defined by the formula:

(Sr.sub.1-x Me'.sub.x)(Li.sub.1/4 Me".sub.3/4)O.sub.3, wherein Me' is at least one element selected from the group of Ca, Ba and Pb; Me" is Ta and/or Nb, and x is 0.01-0.50. The preferred transmission levels are obtained over a compositional range for x of 0.01-0.50. When x .ltoreq. 0.01, the ceramic compositions cannot be sintered to a sufficient density, and when x .gtoreq. 0.50, a second phase is produced.

Having generally described the invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limited unless otherwise specified.

EXAMPLES

Various mixtures of SrCO.sub.3, PbO, CaCO.sub.3, BaCO.sub.3, Li.sub.2 CO.sub.3, Ta.sub.2 O.sub.5 were weighed out so as to obtain a series of materials having the formula (Sr.sub.1-x Me'.sub.x) (Li.sub.1/4 Me".sub.3/4)O.sub.3, wherein x is 0-0.60. The components of each composition were mixed well in a ball mill. Each powder mixture was calcined at 1050.degree. C. for 1 hour, and the resulting mass was pulverized into a powder. Then, each powder sample was mixed with polyvinyl alcohol as a binder, and each mixture was compressed into the shape of a plate of 20.sup..phi. x 1 mm at 1 ton/cm.sup.2. The green samples obtained were sintered at 1250.degree. C. for 2 hours in an electric furnace.

By this technique 161 transparent ceramic plates including control samples were prepared. The density (P%), and the transmission characteristics (transparency or transmittivity) T (%) at 700 m.mu. of each of the plates were measured. Both sides of the measured plates were polished to a mirror finish. After the transparency measurement, a silver electrode was baked on each side of the sample plates. The permittivity (dielectric constant) .epsilon. characteristics of each plate were measured at a frequency of 1 MHz as indicated in Table 1. The transmission characteristics of the present ceramic are superior to the transmission characteristics of conventional Al.sub.2 O.sub.3 ceramic.

The present transparent ceramic composition has many advantages when used in the following applications.

(1) It can be used as an optical element for flash lamp tubes and devices which use infrared rays, because the present ceramics exhibit excellent transparency to visible rays and infrared rays. Moreover, the present ceramics can be produced more easily and less expensively than the conventional Al.sub.2 O.sub.3 ceramics.

(2) The present ceramics are used in the substrates of high quality electronic parts which can be applied to integral circuit substrates, for example, if the particular ceramic has excellent electrical properties. Because the present ceramic materials are poreless materials, it is evident that a substrate can be provided with a flat surface which has a roughness less than about one tenth of the wavelength of the light. Both sides of a transparent ceramic substrate can be used as a substrate for complicated circuit devices.

(3) The transparent electro-optic ceramics of the present invention can be used in microwave frequency devices. It is possible to miniaturize circuits by use of the present high dielectric permittivity and low loss ceramics.

TABLE I__________________________________________________________________________ (Sr.sub.1-x Me'.sub.x)(Li.sub.1/4 Me".sub.3/4)O.sub.3 Me' Me" .epsilon. X Ca Ba Pb Nb T(%) (1MHz) .rho. (%)__________________________________________________________________________control 1 0 -- -- -- 1 -- 12 39 97.0control 2 0.005 0.005 -- -- 1 -- 35 39 98.2example 1 0.01 0.01 -- -- 1 -- 40 39 99.5example 2 0.05 0.05 -- -- 1 -- 55 40 99.7example 3 0.1 0.1 -- -- 1 -- 60 41 99.9example 4 0.2 0.2 -- -- 1 -- 58 41 99.8example 5 0.3 0.3 -- -- 1 -- 60 42 99.8example 6 0.4 0.4 -- -- 1 -- 56 42 99.6example 7 0.5 0.5 -- -- 1 -- 40 43 99.0control 3 0.6 0.6 -- -- 1 -- 20 40 98.1example 8 0.02 0.01 0.01 -- 1 -- 48 39 99.0example 9 0.02 0.01 -- 0.01 1 -- 50 39 99.1example 10 0.1 0.05 0.05 -- 1 -- 58 39 99.3example 11 0.1 0.05 -- 0.05 1 -- 55 40 99.1example 12 0.2 0.1 0.1 -- 1 -- 60 40 99.5example 13 0.2 0.1 -- 0.1 1 -- 58 40 99.4example 14 0.3 0.15 0.15 -- 1 -- 65 40 99.6example 15 0.3 0.15 -- 0.15 1 -- 58 41 99.2example 16 0.3 0.1 0.1 0.1 1 -- 60 41 99.5example 17 0.4 0.2 0.2 -- 1 -- 63 40 99.2example 18 0.4 0.1 0.3 -- 1 -- 65 41 99.3example 19 0.4 0.3 0.1 -- 1 -- 62 40 99.1example 20 0.4 0.2 -- 0.2 1 -- 60 41 99.0example 21 0.4 0.1 -- 0.3 1 -- 55 42 99.4example 22 0.4 0.3 -- 0.1 1 -- 64 40 99.2example 23 0.5 0.2 0.3 -- 1 -- 61 41 99.6example 24 0.5 0.3 0.2 -- 1 -- 63 41 99.5example 25 0.5 0.2 -- 0.3 1 -- 59 42 99.3example 26 0.5 0.3 -- 0.2 1 -- 62 42 99.2control 4 0.6 0.3 0.3 -- 1 -- 23 41 98.1control 5 0.6 0.3 -- 0.3 1 -- 20 42 98.4control 6 0.6 0.2 0.2 0.2 1 -- 30 42 98.3control 7 0.005 -- 0.005 -- 1 -- 30 39 97.5control 8 0.005 -- -- 0.005 1 -- 35 39 97.8example 27 0.01 -- 0.01 -- 1 -- 48 39 98.9example 28 0.01 -- -- 0.01 1 -- 50 39 99.0example 29 0.1 -- 0.1 -- 1 -- 50 39 99.0example 30 0.1 -- -- 0.1 1 -- 53 39 99.1example 31 0.2 -- 0.2 -- 1 -- 55 40 99.3example 32 0.2 -- 0.1 0.1 1 -- 56 40 99.2example 33 0.2 -- -- 0.2 1 -- 54 40 99.1example 34 0.3 -- 0.3 -- 1 -- 58 41 99.3example 35 0.3 -- 0.2 0.1 1 -- 55 41 99.0example 36 0.3 -- 0.1 0.2 1 -- 60 41 99.5example 37 0.3 -- -- 0.3 1 -- 59 41 99.5example 38 0.4 -- 0.4 -- 1 -- 65 41 99.5example 39 0.4 -- 0.3 0.1 1 -- 70 41 99.6example 40 0.4 -- 0.2 0.2 1 -- 68 41 99.3example 41 0.4 -- 0.1 0.3 1 -- 60 41 99.2example 42 0.4 -- -- 0.4 1 -- 50 41 99.0example 43 0.5 -- 0.5 -- 1 -- 60 43 99.2example 44 0.5 -- 0.4 0.1 1 -- 65 43 99.3example 45 0.5 -- 0.3 0.2 1 -- 61 43 99.1example 46 0.5 -- 0.2 0.3 1 -- 58 43 99.0example 47 0.5 -- 0.1 0.4 1 -- 43 99.0example 48 0.5 -- -- 0.5 1 -- 43control 9 0.6 -- 0.6 -- 1 -- 35 42 98.5control 10 0.6 -- 0.5 0.1 1 -- 39 42 98.3control 11 0.6 -- 0.4 0.2 1 -- 30 42 98.8control 12 0.6 -- 0.3 0.3 1 -- 20 42 98.4control 13 0.6 -- 0.2 0.4 1 -- 10 42 97.0control 14 0.6 -- 0.1 0.5 1 -- 8 42 97.5control 15 0.6 -- -- 0.6 1 -- 5 42 96.5control 16 0 -- -- -- -- 1 13 37 97.0control 17 0.005 -- 0.005 -- -- 1 30 37 98.0example 49 0.01 -- 0.01 -- -- 1 50 38 99.0example 50 0.1 -- 0.1 -- -- 1 52 38 99.1example 51 0.2 -- 0.2 -- -- 1 53 38 99.3example 52 0.3 -- 0.3 -- -- 1 60 39 99.2example 53 0.4 -- 0.4 -- -- 1 58 39 99.5example 54 0.5 -- 0.5 -- -- 1 60 39 99.1control 18 0.6 -- 0.6 -- -- 1 20 38 98.5control 19 0.005 0005 -- -- -- 1 28 37 98.0example 55 0.01 0.01 -- -- -- 1 50 37 99.1example 56 0.1 0.1 -- -- -- 1 55 38 99.3example 57 0.2 0.2 -- -- -- 1 60 38 99.5example 58 0.3 0.3 -- -- -- 1 65 39 99.1example 59 0.4 0.4 -- -- -- 1 70 39 99.4example 60 0.5 0.5 -- -- -- 1 65 40 99.0control 20 0.6 0.6 -- -- -- 1 15 38 98.7control 21 0.005 -- -- 0.005 -- 1 20 37 98.0example 61 0.01 -- -- 0.01 -- 1 45 37 99.2control 62 0.1 -- -- 0.1 -- 1 48 37 99.3example 63 0.2 -- -- 0.2 -- 1 50 38 99.1example 64 0.3 -- -- 0.3 -- 1 51 39 99.0example 65 0.4 -- -- 0.4 -- 1 48 40 99.6example 66 0.5 -- -- 0.5 -- 1 41 41 99.2control 22 0.6 -- -- 0.6 -- 1 10 50 98.7control 23 0.6 0.3 0.3 -- -- 1 25 38 98.4control 24 0.6 -- 0.3 0.3 -- 1 5 40 98.6control 25 0.6 0.3 -- 0.3 -- 1 10 40 97.3example 67 0.2 0.1 0.1 -- -- 1 65 39 99.7example 68 0.2 0.1 -- 0.1 -- 1 52 39 99.4example 69 0.2 -- 0.1 0.1 -- 1 50 39 99.2example 70 0.3 0.1 0.1 0.1 -- 1 60 39 99.2example 71 0.3 -- 0.1 0.2 -- 1 55 39 99.4example 72 0.3 0.1 -- 0.2 -- 1 53 39 99.1example 73 0.3 0.1 0.2 -- -- 1 70 39 99.6example 74 0.3 -- 0.2 0.1 -- 1 58 39 99.6example 75 0.3 0.2 -- 0.1 -- 1 56 39 99.7example 76 0.3 0.2 0.1 -- -- 1 65 39 99.4control 26 0.6 0.2 0.2 0.2 -- 1 14 39 98.6control 27 0.6 -- 0.3 0.3 -- 1 12 45 98.3control 28 0.6 0.3 -- 0.3 -- 1 16 43 98.9control 29 0.6 0.3 0.3 -- -- 1 20 38 98.7example 77 0.2 0.2 -- -- 0.8 0.2 60 40 99.8example 78 0.2 0.2 -- -- 0.6 0.4 63 40 99.2example 79 0.2 0.2 -- -- 0.4 0.6 62 39 99.4example 80 0.2 0.2 -- -- 0.2 0.8 61 39 99.3example 81 0.4 0.4 -- -- 0.8 0.2 57 42 99.7example 82 0.4 0.4 -- -- 0.6 0.4 60 40 99.6example 83 0.4 0.4 -- -- 0.4 0.6 65 40 99.3example 84 0.4 0.4 -- -- 0.2 0.8 69 39 99.5control 30 0.6 0.6 -- -- 0.8 0.2 30 40 98.5control 31 0.6 0.6 -- -- 0.6 0.4 35 40 98.8control 32 0.6 0.6 -- -- 0.4 0.6 25 39 99.7control 33 0.6 0.6 -- -- 0.2 0.8 20 39 98.6example 85 0.2 -- 0.2 -- 0.8 0.2 57 41 99.4example 86 0.2 -- 0.2 -- 0.6 0.4 55 40 99.5example 87 0.2 -- 0.2 -- 0.4 0.6 54 39 99.3example 88 0.2 -- 0.2 -- 0.2 0.8 53 39 99.3example 89 0.4 -- 0.4 -- 0.8 0.2 66 41 99.6example 90 0.4 -- 0.4 -- 0.6 0.4 64 41 99.7example 91 0.4 -- 0.4 -- 0.4 0.6 62 40 99.4example 92 0.4 -- 0.4 -- 0.2 0.8 60 40 99.6control 34 0.6 -- 0.6 -- 0.8 0.2 40 41 98.6control 35 0.6 -- 0.6 -- 0.6 0.4 40 40 98.4control 36 0.6 -- 0.6 -- 0.4 0.6 35 40 98.3control 37 0.6 -- 0.6 -- 0.2 0.8 36 39 98.4example 93 0.2 -- -- 0.2 0.8 0.2 55 42 99.3example 94 0.2 -- -- 0.2 0.6 0.4 52 40 99.3example 95 0.2 -- -- 0.2 0.4 0.6 50 40 99.2example 96 0.2 -- -- 0.2 0.2 0.8 50 39 99.2example 97 0.4 -- -- 0.4 0.8 0.2 55 42 99.7example 98 0.4 -- -- 0.4 0.6 0.4 53 41 99.5example 99 0.4 -- -- 0.4 0.4 0.6 51 41 99.4example 100 0.4 -- -- 0.4 0.2 0.8 50 40 99.7control 38 0.6 -- -- 0.6 0.8 0.2 15 43 96.7control 39 0.6 -- -- 0.6 0.6 0.4 10 46 97.0control 40 0.6 -- -- 0.6 0.4 0.6 8 48 97.5control 41 0.6 -- -- 0.6 0.2 0.8 7 49 98.0example 101 0.3 0.1 0.1 0.1 0.8 0.2 62 40 99.7example 102 0.3 0.1 0.1 0.1 0.6 0.4 60 40 99.3example 103 0.3 0.1 0.1 0.1 0.4 0.6 58 39 99.0example 104 0.3 0.1 0.1 0.1 0.2 0.8 59 39 99.1control 42 0.6 0.2 0.2 0.2 0.8 0.2 28 43 98.5control 43 0.6 0.2 0.2 0.2 0.6 0.4 26 41 98.0control 44 0.6 0.2 0.2 0.2 0.4 0.6 20 41 98.0control 45 0.6 0.2 0.2 0.2 0.2 0.8 10 40 98.3example 105 0.2 -- 0.1 0.1 0.8 0.2 58 41 99.3example 106 0.2 -- 0.1 0.1 0.6 0.4 56 41 99.2example 107 0.2 -- 0.1 0.1 0.4 0.6 54 40 99.1example 108 0.2 -- 0.1 0.1 0.2 0.8 52 40 99.0example 109 0.2 0.1 -- 0.1 0.8 0.2 60 41 99.5example 110 0.2 0.1 -- 0.1 0.6 0.4 62 40 99.3example 111 0.2 0.1 -- 0.1 0.4 0.6 57 40 99.3example 112 0.2 0.1 -- 0.1 0.2 0.8 53 39 99.3example 113 0.2 0.1 0.1 -- 0.8 0.2 65 41 99.7example 114 0.2 0.1 0.1 -- 0.6 0.4 63 40 99.4example 115 0.2 0.1 0.1 -- 0.4 0.6 62 40 99.5example 116 0.2 0.1 0.1 -- 0.2 0.8 64 40 99.7__________________________________________________________________________

Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the scope or spirit of the invention as set forth herein.

Claims

1. A transparent, single phase, complex oxide ceramic material of the formula (Sr.sub.1-x Ca.sub.x)(Li.sub.1/4 Nb.sub.3/4)O.sub.3 wherein x is 0.01-0.50.

2. A process for preparing a transparent, single phase, complex oxide ceramic material of the formula (Sr.sub.1-x Ca.sub.x)(Li.sub.1/4 Nb.sub.3/4)O.sub.3 wherein x is 0.01-0.50 comprising:

blending the metal oxide components of transparent, complex oxide ceramic material with a binder;

shaping and pressing said blended materials under 0.5-2 ton/cm.sup.2 ;

and sintering said shaped material under an atmosphere of oxygen at 1150.degree.-1450.degree. C. for 2-4 hours.