3,702,888 United States Patent 0 ” ICC Patented Nov. 14, 1972 .1 2 stoichiometric quantities, i.e., 2 mole equivalents of tel 3,702,888 lurium dioxide to 1 mole equivalent of the second re MICACEOUS TELLURITES AND THE METHOD agent. The second reagent may be any compound con OF MAKING THEM Michael J. Redman, Belmont, Mass., assignor to taining oxygen and an element selected from cadmium, Kennecott Copper Corporation, New York, N.Y. calcium or strontium capable of decomposing to the cad No Drawing. Filed Nov. 5, 1970, Ser. No. 87,337 mium, calcium or strontium oxide at the melt temperature Int. Cl. Clllf 11/00; C01b 19/00 without changing the valence of the tellurium, or the US. Cl. 423-508 10 Claims oxide of cadmium, calcium or strontium. Up to about a 20% excess above the stoichiometric quantity of tellurium 10 dioxide can be tolerated in the reaction and up to about ABSTRACT OF THE DISCLOSURE 10% excess above stoichiometric quantity of the second Tellurites with the composition MTe2O5 where M is reagent can be tolerated. If an excess of one of the re selected from cadmium, strontium, or calcium in the form agents is used the excess of that reagent appears between of mica-like plates are provided. the plate-like layers of the compound. This excess can be 15 mechanically removed or can be removed by using a dilute mineral acid. For many commercial or industrial The present invention relates to novel ternary composi applications the excess of any reagent will not have to be tions of matter. More particularly, it relates to novel removed from the micaceous compounds. mica-like materials which contain three elements, namely, After the tellurium dioxide and the second reagent, i.e., tellurium, oxygen and an element selected from cadmi 20 the compound containing cadmium, calcium, or strontium um, strontium, and calcium. Still more particularly, the capable of decomposing to the respective oxide at the invention is concerned with compounds which possess melt temperature without reducing or oxidizing the tel the composition: lurium IV or the oxide of cadmium, calcium or strontium, MTe2O5 are mixed, the mixture is heated to a temperature of pref~ 25 erably not more than 100° C. above the melting point. where M is the element cadmium, strontium, or calcium. The reaction may proceed at as little as 10 to 20° C. The invention is also concerned with the process of mak above the melting point but the preferable operating ing the mica-like materials possessing the above com temperature is about 50° above the melting point. This position. temperature gives a good ?uidity to the melt and assures The known micas are a series of silicate minerals char 30 intimate mixing and a complete reaction. All that is acterized speci?cally by a perfect basal cleavage. They necessary is that the temperature is enough above the generally yield, with ease, thin tough laminas that have a melting point to give good dissolution and reaction. How high degree of ?exibility. The various micas are struc ever, the temperature should not be so high as to cause turally similar, although the chemical composition may loss of the reagents through volatile losses. vary widely, particularly in the rarer species. Both natural 35 The melt is then held at a temperature of from about micas and synthetic micas are known. Muscovite, the most 10 to 100° C. above the melting point for a period of widely used mica in the electrical industry, has the chem— time up to 12 hours or more to provide a complete ical formula K2A14(Al2Si6Oz0) (OH)4. Phlogopite and bio reaction. Generally a period of time from about 1 to 4 tite are other natural micas. Known synthetic micas in hours is sufficient to complete the reaction. clude ?uorophlogopite and barium disilicic. 40 After remaining at the reaction temperature for the The micas, both synthetic and natural, have found a selected period of time the melt is cooled at a rate of variety of industrial and commercial uses. The higher from about 1 to 20° C. per hour and preferably from qualities of block mica are used principally in the manu about 4 to 8° C. per hour through the melting point facture of electronic tubes, high temperature steam gauge to give the mica-like composition of matter. glasses, and regulator diaphragms. Lower qualities of 45 EXAMPLE 1 block mica are used as electrical insulation in household appliances, incandescent lamps, fuse plugs, and other This example illustrates the preparation of a composi electrical equipment. Film mica is used principally as a tion of matter possessing the composition CdTe2O5. Cad dielectric in capacitors, particularly for the electronic in mium oxide and tellurium dioxide are weighed out in dustry. 50 stoichiometric amounts, i.e., 1:2 molar ratio, ground, The novel compositions of matter of this invention will mixed together and melted in a platinum crucible at also ?nd application in the aforementioned uses. How 750° C. in an electric furnace. The melt was kept at ever, because of the physical properties, particularly the 750° C. for about 3 hours and then the furnace tempera optical properties and dielectric properties, the mica-like ture was dropped at a rate of 4 to 8° C. per hour through tellurites may ?nd additional specialized application such 55 the melting point of 670° to about 600° C. at which tem as in Window material for both visible and infrared light, perature the furnace power was turned off. After cool high energy heavy-ion track detector and as substrate ing in the furnace to room temperature, the platinum cru material in thin ?lm work. cible was removed from the furnace. The resulting mate The reagents used in making the micaceous tellurites rial exhibited a mass of CdTe2O5 plates. The melting of this invention are tellurium dioxide and any compound 60 point of CdTe2O5 is about 670° C. Other physical prop containing cadmium, calcium or strontium that is capable erties are indicated in Tables I and H below. of decomposing to the oxide at the melt temperature with Analysis of the CdTGzOr out reducing or oxidizing the tellurium IV. The preferred Tellurium reagents are the carbonates of cadmium, calcium and Cadmium (wt. percent) (wt. percent) 'I‘eOa (wt. percent) 65 strontium. Of course the oxides of strontium, cadmium 57.07 Net detected. and calcium may be used. 57. 00 Do. 57. 00 D0. In the ?rst step of the process of this invention the (57‘. 02) (Calcd. for CdTezOs). reagents are ground and mixed. It is preferred to use 3,702,888 4 EXAMPLE 2 intensities being estimated visually from ?lms. From . _ these interplanar spacings, the dimensions of the sub p1§h8§§eif§$§°§q%iv§i§§€"§f‘iili‘iféi‘?dc?’bg?itixi?‘d ccllc cl ccTczos cncl ClTcZO-S hcvc llccll cclcclclcd and two molar equivalents of tellurium dioxide are ground and :31igi?l?egzggasiiiezbove’ together wlth the measured mixed. The mixture is placed in an electric furnace in a 5 ' platinum crucible and heated to about 750° C. and held at this temperature for about 3 hours. The furnace tem- TABLE III-—X-RAY DIFFRAC'I‘ION POWDER DATA FOR perature was then dropped at a rate between 4 to 8° C. MICA'LIKE TELLURITES per hour to about 600° C. and the furnace power turned 10 sub- CdTezOs _ 021116205 Symon off. After cooling‘ to room temperature in' the furnace, True ceHHKL cellhkl MA) I (MA) I (KAI) I micaceous SrTe2O5 was removed. The melting point of SrTe2O5 was 680” C. Other physical properties are given in Tables I and II below. EXAMPLE 3 CaTe2O5 was prepared by grinding and mixing stoichio metric quantities of calcium carbonate and tellurium di oxide, heating the mixture in a platinum crucible in an elec tric furnace to a temperature of about 850° C. and hold ing at this temperature for about 3 hours. The furnace was then cooled at a rate of from about 4 to 8° C. per hour until a furnace temperature of about 700° C. had been reached and the furnace power shut off. The plate-like CaTe2O5 compound was removed from the furnace after cooling down to room temperature. The melting point of CaTe-2O5 was about 792° C. Other physical properties are shown in Tables I and II below. TABLE I.—MELTING POINTS, DENSITIES AND SUB CELL PARAMETERS 0F MICA<LIKE TELLURITES1 Physical quantity CdTezO5 Ca’I‘ezOs Sr'I‘e101 Melting point (° C.) .............. _. 670 (5) 792 (5) 680 (5) Meats. density (gt/cm?). 6.2 ( 6! (deg) ............ -_ Sub-cell volume (A.ll)_ Cale. density (gJcmJ) ____________ __ lEstimated errors in the least signi?cant ?gures are given in parentheses. Z03 ------------ - — 114 1 674 5 .......................... .. of The25° ‘dielectricC. and 95° properties C. by means were of measured a three terminalat temperatures capaci- 522 1 660 5 1.674 a 1 677 15 tance bridge covering a frequency range of 100 Hz. to 10 301 kHz). The samples studied were in the form of thin sheets 304+ 1- 634 10 1-647 5 1-651 3 approximately 0.005-0.01 cm. thick, upon ‘which circular silver electrodes were evaporated. The DC. resistivity was 1- 610 15 1- 626 10 1. 636 5 measured with a Keithley electrometer. 1. 590 5 1. 604 2 1. 617 1 The micaceous-like materials of this invention are op 1. 545 5 1. 553 3 ____________ __ tically biaxial (-—), with an optic axial angle of 2V: 30° 312 496 2 for CdTe2O5 and with the lowest index n06 perpendicular 00 1 ' ___________________ " to the cleavage plane.