Thermistor composition

The invention is directed to a thick film thermistor composition consisting of finely divided particles of (a) a ruthenium-based pyrochlore, and (b) a short borosilicate glass or glass mixture, both dispersed in (c) an organic medium.

FIELD OF INVENTION 
The invention is directed to thick film thermistor compositions. 
BACKGROUND OF THE INVENTION 
The term "thermistor" is the generic name for devices made from materials 
the electrical conductivity of which is highly sensitive to variations in 
temperature. While thermistors are widely used as temperature sensors in a 
wide variety of industrial and consumer applications, they are 
particularly useful as elements of electric and electronic circuits. 
Thermistors having positive temperature coefficients (PTC thermistors) as 
well as thermistors having negative temperature coefficients (NTC 
thermistors) are used. Previously, thermistors having a high positive 
temperature coefficient of resistance (TCR) have been available, but the 
resistance range of those materials has been limited. Thus, the design 
flexibility of highly positive thermistors has been limited also. For 
example, doped BaTiO.sub.3 has a high positive TCR, but the useful range 
of temperatures is only between room temperature and 100.degree. C. Metals 
have a highly positive TCR but are limited in their usefulness by their 
low resistivity. On the other hand, silicon crystals, which do have both a 
highly positive TCR and a wide temperature range, can't be screen printed 
and therefore are limited in their usefulness also. In addition, RuO.sub.2 
and RuO.sub.2 derivatives are known to have a good temperature range, but 
heretofore have had only small positive TCR values. 
SUMMARY OF THE INVENTION 
Therefore, the invention in its primary aspect is directed to thick film 
thermistor compositions based on ruthenium-based pyrochlores which produce 
fired thermistors which have high positive TCR values over a wide 
temperature range. In particular, the invention is directed to a thick 
film composition comprising an admixture of finely divided particles of 
(a) 5-60% wt. of a ruthenium-based pyrochlore; (b) 95-40% wt. of a 
borosilicate glass or mixture of glasses containing by mole %, basis total 
glass, (1) 65-85% glass-forming oxides containing 25-55% B.sub.2 O.sub.3, 
40-10% SiO.sub.2 and 30-0% other glass-forming oxides selected from 
Al.sub.2 O.sub.3, Bi.sub.2 O.sub.3, ZrO.sub.2 and mixtures thereof, and 
(2) 35-15% glass-modifying oxides consisting essentially of 3-35% alkaline 
earth metal oxide(s) of which no more than about 10% is MgO and 0-28% 
replacement oxide(s) selected from Cu2O, PbO, ZnO and mixtures thereof, of 
which none exceeds 10% and the total of which does not exceed 80% of the 
total glass modifying oxides, the viscosity of the glass upon firing at a 
peak temperature of 700.degree.-1000.degree. C. being from 10 to 10,000 
poises, both of components (a) and (b) being dispersed in (c) an organic 
medium.

DETAILED DESCRIPTION OF THE INVENTION 
A. Ruthenium-Based Pyrochlore 
The invention is directed to thermistors in which the principal conductive 
phase is ruthenium pyrochlore-based. At the present state of the art, this 
is known to include ruthenium compounds corresponding to the formula 
(M.sub.c Bi.sub.2-c)M'.sub.d Ru.sub.2-d)O.sub.7-e, wherein 
M is at least one of the group consisting of yttrium, thallium, indium, 
cadmium, lead and the rare earth metals of atomic number 57-71 inclusive; 
M' is at least one of platinum, titanium, chromium, rhodium and antimony; 
c is a number in the range 0 to 2; 
d is a number in the range 0 to about 0.5, provided that d is a number in 
the range 0 to 1 when M' is rhodium or more than one of platinum, and 
titanium; and 
e is a number in the range 0 to 1, being at least equal to about c/2 when M 
is divalent lead or cadmium. 
These compounds and their preparation are disclosed in U.S. Pat. No. 
3,583,931 to Bouchard and also in German Patent Application OS 1,816,105. 
The metal-rich ruthenium-based pyrochlores disclosed in the following U.S. 
patents can also be used in the compositions of the invention: U.S. Pat. 
Nos. 4,124,539; 4,129,525; 4,146,458; 4,163,706; 4,176,094; 4,192,780; 
4,203,871; and 4,225,469. 
The particle size of the above-described active materials is not narrowly 
critical from the standpoint of their technical effectiveness in the 
invention. However, they should, of course, be of a size appropriate to 
the manner in which they are applied, which is usually screen printing, 
and to the firing conditions. Thus the metallic material should be no 
bigger than 10 .mu.m and preferably should be below about 5 .mu.m. As a 
practical matter, the available particle size of the metals is as low as 
0.1 .mu.m. It is preferred that the ruthenium component have an average 
surface area of at least 5 m.sup.2 /g and still more preferably at least 8 
m.sup.2 /g. 
Preferred ruthenium compounds include BiPbRu.sub.2 O.sub.6.5, Bi.sub.0.2 
Pb.sub.1.8 Ru.sub.2 O.sub.6.1, Bi.sub.2 Ru.sub.2 O.sub.7, and Pb.sub.2 
Ru.sub.2 O.sub.6. 
B. Inorganic Binder 
In describing the composition of inorganic binders herein, all component 
proportions are given in mole percentages unless expressly indicated 
otherwise. 
The inorganic binder component of the invention is a "short" borosilicate 
glas which when the composition in which it is used is fired at 
700.degree.-1000.degree. C., exhibits a viscosity of 10 to 10,000 poises. 
Unlike so-called "long" glasses, which have higher viscosities when they 
are fired at relatively low temperatures, the "short" glasses, which are 
preferred for use in the compositions of the invention, have rather 
steeply downward viscosity/temperature correlations. Thus the preferred 
"short" glasses are more viscous at low temperatures. Thus they better 
facilitate more complete burnout or organics and minimize the occlusion of 
carbon particles which may be derived from the burnout of organics. The 
glasses which are effective for use in the invention can, however, be 
amorphous (vitreous) or crystalline (non-vitreous). 
Compositionally, the glasses for use in the invention are borosilicate 
glasses which contain by mole % 65-85% glass-forming oxides and 35-15% 
glass-modifying oxides. These limis are important with respect to their 
performance in thermistor compositions. In particular, if less than 15% 
glass modifiers are used, they are insufficient to form a stable vitreous 
state. However, if more than about 35% glass modifiers are used, the glass 
is not durable enough and the TCE is likely to become excessive. 
The primary glass-forming oxides are B.sub.2 O.sub.3 which is used at a 
concentration of 25-55% of the glass and SiO.sub.2 which is used at a 
concentration of 40 to 10% of the glass. The glass should contain at least 
25% B.sub.2 O.sub.3 to ensure that the viscosity of the glass during 
firing is not excessively high. However, if the B.sub.2 O.sub.3 content is 
higher than about 55%, the durability of the glass is likely to be reduced 
to unacceptable levels. 
The glass may also contain conditional glass-forming oxides up to a 
concentration of 30%. Such conditional glass-forming oxides include 
Al.sub.2 O.sub.3, Bi.sub.2 O.sub.3, ZrO.sub.2 and mixtures thereof. While 
these conditional glass-forming oxides are not considered essential for 
all applications of the invention, it is nevertheless preferred that the 
glass contain at least about 10% and preferably 15% of such secondary 
glass-forming oxides. In particular, Bi.sub.2 O.sub.3 is desirable to 
lower viscosity of the glass and enhance the glass firing range. On the 
other hand, Al.sub.2 O.sub.3 is desirable not only to enhance the 
glass-forming range, but also improve its durability. 
The primary glass modifiers for use in the glasses of the invention are the 
alkaline earth metal oxides which can be used in amounts up to 35% of the 
total glass. The alkaline earth metal oxides can be used either 
individually or in admixture. However, it is preferred that no more than 
10% MgO be used, lest the glass tend to crystallize when it is subjected 
to thick film processing conditions. Up to 80% of the primary alkaline 
earth metal oxide glass modifiers can be substituted by secondary or 
substitute glass modifiers such as ZnO, PbO, Cu.sub.x O (Cu.sub.2 O or 
CuO) or ZrO.sub.2. However, the glass binder should contain no more than 
15% wt. of any of these substitute glass formers, lest the viscosity of 
the glass at firing temperature become too high. 
In addition to the glass itself, the composition of the invention can 
contain small amounts (up to 15% wt.) of CuO, Cu.sub.2 O and/or ZrO.sub.2 
or precursors thereof to enhance the hot TCR of the composition. 
In the practice of the invention, it has been shown by x-ray diffraction 
studies that the ruthenium-based pyrochlore component is essentially 
completely decomposed to RuO.sub.2 and the other oxide components of the 
pyrochlore are absorbed into the glass during the firing operation. 
However, when RuO.sub.2 is substituted for the ruthenium-based pyrochlore, 
the properties of the fired composition are quite different. For example, 
the composition of the invention when fired results in a thermistor having 
a highly positive TCR value, whereas a conventional RuO.sub.2 -based 
composition results in moderately negative TCR values and lower R values. 
Thus, even though the primary conductive component of the final 
compositions are the same, the electrical properties are quite different. 
Though the reason for this apparent anomaly is not fully understood, it is 
believed that the decomposition products of the pyrochlore may be 
interacting with the glass binder to influence these results. 
The glasses are prepared by conventional glass-making techniques by mixing 
the desired components in the desired proportions and heating the mixture 
to form a melt. As is well known in the art, heating is conducted to a 
peak temperature and for a time such that the melt becomes entirely liquid 
and homogeneous. In the present work, the components are premixed by 
shaking in a polyethylene jar with plastic balls and then melted in a 
crucible at up to 1200.degree. C., depending on the composition of the 
glass. The melt is heated at a peak temperature for a period of 1-3 hours. 
The melt is then poured into cold water. The maximum temperature of the 
water during quenching is kept as low as possible by increasing the volume 
of water to melt ratio. The crude frit after separation from water is 
freed from residual water by drying in air or by displacing the water by 
rinsing with methanol. The crude fruit is then ball-milled for 3-5 hours 
in alumina containers using alumina balls. Alumina picked up by the 
materials, if any, is not within the observable limit as measured by x-ray 
diffraction analysis. 
After discharging the milled frit slurry from the mill, the excess solvent 
is removed by decantation and the frit powder is air dried at room 
temperature. The dried powder is then secured through a 325-mesh screen to 
remove any large particles. 
The major two properties of the frit are: it aids the liquid phase 
sintering of the inorganic crystalline particulate matters and form 
noncrystalline (amorphous) or crystalline materials by devitrification 
during the heating-cooling cycle (firing cycle) in the preparation of 
thick film resistors. This devitrification process can yield either a 
single crystalline phase having the same composition as the precursor 
noncrystalline (glassy) material or multiple crystalline phases with 
different compositions from that of the precursor glassy material. 
C. Organic Medium 
The inorganic particles are mixed with an essentially inert liquid medium 
(vehicle) by mechanical mixing (e.g., on a roll mill) to form a pastelike 
composition having suitable consistency and rheology for screen printing. 
The latter is printed as a "thick film" on conventional dielectric 
substrates in the conventional manner. 
Any inert liquid may be used as the vehicle. Various organic liquids, with 
or without thickening and/or stabilizing agents and/or other common 
additives, may be used as the vehicle. Exemplary of organic liquids which 
can be used are the aliphatic alcohols, esters of such alcohols, for 
example, acetates and propionates, terpenes such as pine oil, terpineol 
and the like, solutions of resins such as the polymethacrylates of lower 
alcohols and solutions of ethyl cellulose in solvents such as pine oil and 
the monobutyl ether of ethylene glycol monoacetate. A preferred vehicle is 
based on ethyl cellulose and beta-terpineol. The vehicle may contain 
volatile liquids to promote fast setting after application to the 
substrate. 
The ratio of vehicle to solids in the dispersions can vary considerably and 
depends upon the manner in which the dispersion is to be applied and the 
kind of vehicle used. Normally to achieve good coverage, the dispersions 
will contain complementally 60-90% solids and 40-10% vehicle. The 
compositions of the present invention may, of course, be modified by the 
addition of other materials which do not affect its beneficial 
characteristics. Such formulation is well within the skill of the art. 
The pastes are conveniently prepared on a three-roll mill. The viscosity of 
the pastes is typically within the following ranges when measured on a 
Brookfield HBT viscometer at low, moderate and high shear rates: 
______________________________________ 
Shear Rate (sec.sup.-1) 
Viscosity (Pa .multidot. s) 
______________________________________ 
0.2 100-5000 
300-2000 Preferred 
600-1500 Most Preferred 
4 40-400 
100-250 Preferred 
140-200 Most Preferred 
384 7-40 
10-25 Preferred 
12-18 Most Preferred 
______________________________________ 
The amount of vehicle utilized is determined by the final desired 
formulation viscosity. 
FORMULATION AND APPLICATION 
In the preparation of the composition of the present invention, the 
particulate inorganic solids are mixed with the organic carrier and 
dispersed with suitable equipment, such as a three-roll mill, to form a 
suspension, resulting in a composition for which the viscosity will be in 
the range of about 100-150 pascal-seconds at a shear rate of 4 sec.sup.-1. 
In the examples which follow, the formulation was carried out in the 
following manner: 
The ingredients of the paste, minus about 5% organic components equivalent 
to about 5% wt., are weighted together in a container. The components are 
then vigorously mixed to form a uniform blend; then the blend is passed 
through dispersing equipment, such as a three-roll mill, to achieve a good 
dispersion of particles. A Hegman gauge is used to determine the state of 
dispersion of the particles in the paste. This instrument consists of a 
channel in a block of steel that is 25 .mu.m deep (1 mil) on one end and 
ramps up to 0" depth at the other end. A blade is used to draw down paste 
along the length of the channel. Scratches will appear in the channel 
where the agglomerates' diameter is greater than the channel depth. A 
satisfactory dispersion will give a fourth scratch point of 10-18 
typically. The point at which half of the channel is uncovered with a well 
dispersed paste is between 3 and 8 typically. Fourth scratch measurement 
of &gt;20 .mu.m and "half-channel" measurements of &gt;10 .mu.m indicate a 
poorly dispersed suspension. 
The remaining 5% consisting of organic components of the paste is then 
added, and the resin content is adjusted to bring the viscosity when fully 
formulated to between 140 to 200 Pa.s at a shear rate of 4 sec.sup.-1. The 
composition is then applied to a substrate, such as alumina ceramic, 
usually by the process of screen printing, to a wet thickness of about 
30-80 microns, preferably 35-70 microns, and most preferably 40-50 
microns. The electrode compositions of this invention can be printed onto 
the substrates either by using an automatic printer or a hand printer in 
the conventional manner, preferably automatic screen stencil techniques 
are employed using a 200- to 325-mesh screen. The printed pattern is then 
dried at below 200.degree. C., about 150.degree. C., for about 5-15 
minutes before firing. Firing to effect sintering of both the inorganic 
binder and the finely divided particles of metal is preferably done in a 
well ventilated belt conveyor furnace with a temperature profile that will 
allow burnout of the organic matter at about 300.degree.-600.degree. C., a 
period of maximum temperature of about 700.degree.-1000.degree. C. lasting 
about 5-15 minutes, followed by a controlled cooldown cycle to prevent 
over sintering, unwanted chemical reactions at intermediate temperatures 
or substrate fracture which can occur from too rapid cooldown. The overall 
firing procedure will preferably extend over a period of about 1 hour, 
with 20-25 minutes to reach the firing temperature, about 10 minutes at 
the firing temperature and about 20-25 minutes in cooldown. In some 
instances, total cycle times as short as 30 minutes can be used. 
SAMPLE PREATION 
Samples to be tested for Temperature Coefficient of Resistance (TCR) are 
prepared as follows: 
A pattern of the thermistor formulation to be tested is screen printed upon 
each of ten coded Alsimag 614 1.times.1" ceramic substrates and allowed to 
equilibrate at room temperature and then dried at 150.degree. C. The mean 
thickness of each set of dried films before firing must be 22-28 microns 
as measured by a Brush Surfanalyzer. The dried and printed substrate is 
then fired for about 60 minutes using a cycle of heating at 35.degree. C. 
per minute to 850.degree. C., dwell at 850.degree. C. for 9 to 10 minutes 
and cooled at a rate of 30.degree. C. per minute to ambient temperature. 
RESISTANCE MEASUREMENT AND CALCULATIONS 
The test substrates are mounted on terminal posts within a controlled 
temperature chamber and electrically connected to a digital ohm-meter. The 
temperature in the chamber is adjusted to 25.degree. C. and allowed to 
equilibrate, after which the resistance of each substrate is measured and 
recorded. 
The temperature of the chamber is then raised to 125.degree. C. and allowed 
to equilibrate, after which the resistance of the substrate is again 
measured and recorded. 
The temperature of the chamber is then cooled to -55.degree. C. and allowed 
to equilibrate and the cold resistance measured and recorded. 
The hot temperature coefficient of resistance (HTCR) and cold temperature 
coefficient of resistance (CTCR) are calculated as follows: 
##EQU1## 
The values of R.sub.25.degree. C. and Hot TCR are averaged and 
R.sub.25.degree. C. values are normalized to 25 microns dry printed 
thickness and resistivity is reported as ohms per square at 25 microns dry 
print thickness. Normalization of the multiple test values is calcuated 
with the following relationship: 
##EQU2## 
EXAMPLES 
In the Examples which follow, all thick film compositions and inorganic 
binders were prepared and the final thermistors therefrom were tested in 
the manner described hereinabove. 
In Table I, the composition of the four glasses in accordance with the 
invention are given. 
Thus, the following Examples differ only in their composition as indicated 
in the Tables. 
TABLE I 
______________________________________ 
Preferred Glass Compositions 
Glass No. 
1 2 3 4 
Composition (Mole %) 
______________________________________ 
Glass Former 
Al.sub.2 O.sub.3 
5.0 -- 4.3 4.3 
B.sub.2 O.sub.3 
55.0 55.0 47.3 42.3 
Bi.sub.2 O.sub.3 
-- -- -- 5.0 
SiO.sub.2 15.0 20.0 17.4 17.4 
ZrO.sub.2 -- -- 4.5 4.5 
Sub-Total 75.0 75.0 73.5 73.5 
Glass Modifier 
BaO 20.0 10.0 17.2 17.2 
CaO -- -- -- -- 
MgO 5.0 5.0 2.1 2.1 
SrO -- 10.0 -- -- 
Sub-Total 25.0 25.0 19.3 19.3 
PbO -- -- -- -- 
ZnO -- -- 6.7 6.7 
CuO -- -- 0.5 0.5 
Sub-Total -- -- 7.2 7.2 
______________________________________ 
TABLE II 
______________________________________ 
Effect of Pyrochlore Concentration 
on Thermistor Electrical Properties 
______________________________________ 
Example No. 
1 2 3 4 
Composition (% Wt.) 
______________________________________ 
Glass No. 1 60.0 70.0 80.0 85.0 
Pb.sub.2 Ru.sub.2 O.sub.6 
40.0 30.0 20.0 15.0 
RuO.sub.2 -- -- -- -- 
ZrSiO.sub.4 -- -- -- -- 
Electrical Properties 
R.sub.av (.OMEGA./.quadrature.) 
55 218 1419 3423 
HTCR.sub.av (ppm/.degree.C.) 
1730 1242 700 536 
______________________________________ 
Example No. 
5 6 7 8 
Composition (% Wt.) 
______________________________________ 
Glass No. 1 90.0 91.0 96.3 80.0 
Pb.sub.2 Ru.sub.2 O.sub.6 
10.0 9.0 -- 10.0 
RuO.sub.2 -- -- 3.7 -- 
ZrSiO.sub.4 -- -- -- 10.0 
Electrical Properties 
R.sub.av (.OMEGA./.quadrature.) 
10392 23502 210086 7795290 
HTCR.sub.av (ppm/.degree.C.) 
376 288 22 -105 
______________________________________ 
Examples 1-6 illustrate the effect of increasing lead ruthenate content 
upon the electrical properties of the thermistors of the invention. In 
particular, as the concentration of lead ruthenate is raised, HTCR rises 
rapidly and becomes most highly positive. Examination of the fired 
thermistors by x-ray diffraction revealed diffraction lines only for 
RuO.sub.2 and not Pb.sub.2 Ru.sub.2 O.sub.6. Yet a comparison of Examples 
3 and 7 which contain the same equivalent amount of RuO.sub.2 shows that 
the thermistors containing added RuO.sub.2 only (Example 7) had resistance 
values which were almost two orders of magnitude higher than those in 
which the RuO.sub.2 was derived from the Pb.sub.2 Ru.sub.2 O.sub.6 upon 
firing. In addition, HTCR was much lower, albeit still slightly positive, 
for the fired compositions containing added RuO.sub.2. 
A comparison of Example 8 with Example 5 shows that the addition of a 
zircon (ZrSiO.sub.4) filler causes a very steep increases in resistance 
and a decrease in HTCR which becomes negative. It is believed that upon 
firing some of the ZrSiO.sub.4 becomes dissolved in the binder glass and 
thus raises its viscosity. 
EXAMPLES 9-12 
TABLE III 
______________________________________ 
Effect of Additives on 
Thermistor Electrical Properties 
Example No. 
9 10 11 12 
Composition (% Wt.) 
______________________________________ 
Glass No. 1 90.0 80.0 80.0 76.5 
Pb.sub.2 Ru.sub.2 O.sub.6 
10.0 10.0 10.0 10.0 
ZrSiO.sub.4 -- 10.0 -- 8.0 
ZnO.sup.- -- -- 10.0 4.5 
CuO -- -- -- 1.0 
Electrical Properties 
R.sub.av (.OMEGA./.quadrature.) 
10.4 7795.3 8.8 173.3 
HTCR.sub.av (ppm/.degree.C.) 
376 -105 240 318 
______________________________________ 
Examples 9-12 (data in Table III above) all contain the same amount of 
pyrochlore, but part of the glass binder was substituted with a metal 
oxide filler (note that Example 9 is the same as Example 5 supra and 
Examples 10 is the same as Example 8 supra). Example 10 shows that the use 
of ZrSiO.sub.4 raises resistance and lower TCR. Example 11 illustrates the 
effect of ZnO in raising resistance and somewhat lowering TCR. Example 12 
shows that by using a combination of CuO and ZnO, thermistors of 
equivalent TCR value can be made with greatly different resistance values. 
The fillers also affect the firing viscosity of the composition in that 
ZrSiO.sub.4 raises glass viscosity and ZnO lowers glass viscosity. 
EXAMPLES 13-18 
TABLE IV 
______________________________________ 
Use of Mixed Glasses 
In Thermistor Compositions 
______________________________________ 
Example No. 
13 14 15 16 
Composition (% Wt.) 
______________________________________ 
Glass No. 3 65.0 53.9 70.0 60.0 
Glass A.sup.(1) 
10.0 15.0 10.0 20.0 
Pb.sub.2 Ru.sub.2 O.sub.6 
20.0 20.0 20.0 15.0 
ZrSiO.sub.4 5.0 7.1 -- 5.0 
Electrical Properties 
R.sub.av (k.OMEGA./.quadrature.) 
889 10 7 6452 
HTCR.sub.av (ppm/.degree.C.) 
173 690 489 .sup.(2) 
______________________________________ 
Example No. 
17 18 
Composition (% Wt.) 
______________________________________ 
Glass No. 3 50.0 45.0 
Glass A.sup.(1) 30.0 40.0 
Pb.sub.2 Ru.sub.2 O.sub.6 
15.0 15.0 
ZrSiO.sub.4 5.0 -- 
Electrical Properties 
R.sub.av (k.OMEGA./.quadrature.) 
10 1 
HTCR.sub.av (ppm/.degree.C.) 
1206 1824 
______________________________________ 
.sup.(1) 65% wt. PbO, 34.0% wt. SiO.sub.2, 1.0% wt. Al.sub.2 O.sub.3 
.sup.(2) Unstable 
The data in Table IV show the effect of changing the ratio of lead-free 
glass (Glass No. 3) to lead-containing glass (Glass A) on the thermistor 
properties. In particular, Examples 13 and 14 show that as the amount of 
PbO is raised, the resistance drops even when the concentration of filler 
(ZrSiO.sub.4) is higher and the TCR becomes more positive as well. 
Examples 13 and 15 show that the user of filler raises resistance and 
lowers TCR values. Nevertheless, a comparison of Example 14 with Example 
15 and Example 16 with Example 17 show that the use of filler does not 
always raise resistance and lower TCR, but that it depends on the ratio of 
PbO-containing glass to PbO-free glass. 
A comparison of Example 16 and 17 with Example 18 shows that as the amount 
of PbO-containing glass is raised, resistance drops and TCR is raised. 
EXAMPLES 19-26 
TABLE V 
______________________________________ 
Effect of Formulation 
Variables On Thermistor Properties 
______________________________________ 
Example No. 
19 20 21 22 
Composition (% Wt.) 
______________________________________ 
Glass No. 3 -- 85.0 -- -- 
Glass No. 4 85.0 -- 90.0 80.0 
Glass A* -- -- -- 10.0 
Pb.sub.2 Ru.sub.2 O.sub.6 
15.0 15.0 10.0 10.0 
Bi.sub.2 Ru.sub.2 O.sub.7 -- 
RuO.sub.2 -- -- -- 
Electrical Properties 
R.sub.av (k.OMEGA./.quadrature.) 
9.3 ** ** 93.9 
HTCR.sub.av (ppm/.degree.C.) 
1305 -- -- 1465 
______________________________________ 
Example No. 
23 24 25 26 
Composition (% Wt.) 
______________________________________ 
Glass No. 3 84.2 94.4 80.0 70.0 
Glass No. 4 -- -- -- -- 
Glass A* -- -- -- -- 
Pb.sub.2 Ru.sub.2 O.sub.6 
-- -- 20.0 30.0 
Bi.sub.2 Ru.sub.2 O.sub.7 
15.8 -- -- -- 
RuO.sub.2 -- 5.6 -- -- 
-- -- 
Electrical Properties 
R.sub.av (k.OMEGA./.quadrature.) 
81.4 109.7 57.3 1.3 
HTCR.sub.av (ppm/.degree.C.) 
446 -128 224 584 
______________________________________ 
*57.5% wt. PbO, 24.5% wt. SiO.sub.2, 0.8% Al.sub.2 O.sub.3, 16.2% wt. 
B.sub.2 O.sub.3, 1.0% wt. CuO. 
**Too high for measurement 
Comparison of Examples 19 and 20 shows that the use of glass 4 in which a 
small amount of Bi.sub.2 O.sub.3 is substituted for B.sub.2 O.sub.3 
reszults in a lower resistance while use of the bismuth-free glass 
resulted in a resistance value too high for measurement. This phenomenon 
is the result of the reduced viscosity of the Bi.sub.2 O.sub.3 -containing 
glass. 
Example 21 shows that the use of less pyrochlore than in Example 19 results 
in a resistance value too high for measurement. However, by substituting 
10% of Glass A, a useful resistance value is obtained and a good TCR value 
is obtained also. These examples show in addition that by mixing 
composition, such as Example 19 and 22, a range of resistors having R 
values from 10 to 100 K.OMEGA./.quadrature. can be obtained. 
Example 23 illustrates the use of a bismuth ruthenate in place of lead 
ruthenate and that the two ruthenates are fully equivalent in their 
usefulness in the thermistor composition of the invention. 
Example 24 and 25 illustrate a very subtle but important point. In 
particular, even though these two compositions contain the same equivalent 
amount of RuO.sub.2, the fired thermistors do not have the same 
properties. Thus the presence of RuO.sub.2 derived from a ruthenium-based 
pyrochlore is not equivalent to the use of RuO.sub.2 by itself. From these 
data it can be seen that the glass interaction of the composition of the 
invention are quite important. 
Examples 25 and 26, on the other hand, illustrate that raising the level of 
pyrochlore in the composition lowers resistance values and raises positive 
TCR values. 
EXAMPLES 27 and 28 
TABLE VI 
______________________________________ 
Effect of Copper Oxide Addition 
On Electrical Properties of Thermistors 
Example No. 
27 28 
Composition (% Wt.) 
______________________________________ 
Glass No. 4 70.0 65.7 
Glass No. B.sup.(1) 10.0 10.0 
Pb.sub.2 Ru.sub.2 O.sub.6 
20.0 20.0 
Cu.sub.2 O -- 4.3 
Electrical Properties 
Rav(.OMEGA./.quadrature./mil) 
4717 164 
HTCR (ppm/.degree.C.) 
1092 2735 
CTCR (ppm/.degree.C.) 
1228 3122 
______________________________________ 
.sup.(1) 57.5% wt. PbO, 24.5% wt. SiO.sub.2, 0.8% wt. Al.sub.2 O.sub.3, 
16.2% wt. B.sub.2 O.sub.3 and 1.0% wt. Cu.sub.2 O. 
The data in Table VI show that the addition of copper oxide (Cu.sub.2 O) to 
compositions containing the same relative amount of Pb.sub.2 Ru.sub.2 
O.sub.6 results in a substantial increase in both HTCR and CTCR and a 
substantial decrease in resistance. 
EXAMPLES 29-31 
TABLE VII 
______________________________________ 
Effect of Copper Oxide and Zirconium Silicate 
Addition on Electrical Properties of Thermistors 
Example No. 
29 30 31 
Composition (% Wt.) 
______________________________________ 
Glass No. 4 50.0 57.9 62.9 
Glass No. B 10.0 10.0 10.0 
Pb.sub.2 Ru.sub.2 O.sub.6 
22.9 15.0 10.0 
Cu.sub.2 O 10.0 10.0 10.0 
ZrSiO.sub.4 7.1 7.1 7.1 
Electrical Properties 
Rav(.OMEGA./.quadrature./mil) 
57 231 5150 
HTCR (ppm/.degree.C.) 
3219 2998 2379 
CTCR (ppm/.degree.C.) 
2907 2645 2143 
______________________________________ 
In comparing the data in Table VII with the data from Example 27, it can be 
seen that the addition of ZrSiO.sub.4 gives a very sharp increase in both 
HTCR and CTCR and that ZrSiO.sub.4 in combination with Cu.sub.2 O can be 
used to prepare an entire family of thermistors having a wide range of 
electrical properties. 
EXAMPLES 32-34 
TABLE VIII 
______________________________________ 
Use of Fillers and Glass Combinations 
To Obtain a Range of Resistance Properties 
Example No. 
32 33 34 
Composition (% Wt.) 
______________________________________ 
Glass No. 4 22.0 24.7 25.6 
Glass A 26.0 29.3 30.4 
Glass No. B 10.3 10.3 10.3 
Pb.sub.2 Ru.sub.2 O.sub.6 
17.3 11.3 9.3 
Cu.sub.2 O 3.0 3.0 3.0 
ZrSiO.sub.4 14.3 14.3 14.3 
SiO.sub.2 7.1 7.1 7.1 
Electrical Properties 
Rav(k.OMEGA./.quadrature./mil) 
0.9 10.1 215.9 
HTCR (ppm/.degree.C.) 
2528 2668 2397 
CTCR (ppm/.degree.C.) 
3092 3134 3047 
______________________________________ 
The data in Table VIII show that thermistors having a wide range of 
resistance values can be made in accordance with the invention by use of 
glass mixtures. The use of ZrSiO.sub.4 as a filler has essentially no TCR 
effect. Likewise the SiO.sub.2 affects only the viscosity and CTE of the 
fired composition. The Cu.sub.2 O was used to adjust both resistance and 
TCR levels.