High temperature ceramic dielectric composition and capacitors made from the composition
View Patent ↗A bismuth sodium titanate (Bi 0.5 Na 0.5 TiO 3 ) base material is modified by the partial substitution of aliovalent A-site cations such as barium (as BaO) or strontium (as SrO), as well as certain b-site donor/acceptor dopants and sintering aids to form a multi-phase system, much like known “core/shell” X7R dielectrics based solely on BaTiO 3 . The resulting ceramic dielectric composition is particularly suitable for producing a multilayer ceramic capacitor ( 10 ) that maintains high dielectric constant (and thus the capability of maintaining high capacitance) over a broad temperature range of from about 150° C. to about 300° C. Such capacitors ( 10 ) are appropriate for high temperature power electronics applications in fields such as down-hole oil and gas well drilling.
1. A high temperature ceramic dielectric composition suitable for use within a capacitor, the composition comprising:
a. about 98.35 mole % of a calcined base mixture of Me x (Bi 0.5 Na 0.5 ) 1-x TiO 3 , wherein Me is selected from the group consisting of Ba 2+ and Sr 2+ , and wherein X is from between about 0.06 and about 0.12;
b. about 0.88 mole % of at least one oxide of small donor cations, the at least one oxide of small donor cations including an oxide of at least one of Nb 5+ , Ta 5+ , and W 6+ small donor cations;
c. about 0.38 mole % of at least one oxide of acceptor cations;
d. about 0.13 mole % of oxides of large donor cations selected from the group consisting of Nd 2 O 3 , other rare earth oxides, and combinations thereof; and,
e. about 0.26% mole % of a glass forming compound selected from the group consisting of SiO 2 , B 2 0 3 , Ge0 2 , V 2 0 5 , and combinations thereof.
2. The high temperature ceramic dielectric composition of claim 1 , wherein the oxides of small and large donor cations are selected from the group of oxides of small and large donor cations consisting of Nb 5+ , Nd 3+ , Ta 5+ , and W 6+ .
3. The high temperature ceramic dielectric composition of claim 1 , wherein the oxides of small and large donor cations are selected from the group of oxides of small and large donor cations consisting of Nb 5+ , Nd 3+ , Ta 5+ , W 6+ , La 3+ , Pr 3+ , Sm 3+ , Gd 3+ and Ce 4+ .
4. The high temperature ceramic dielectric composition of claim 1 , wherein the about 0.38 mole % of at least one oxide of acceptor cations includes about 0.09 mole % of MnO.
5. The high temperature ceramic dielectric composition of claim 1 , wherein the about 0.38 mole % of at least one oxide of acceptor cations includes about 0.09 mole % of MnO and about 0.29 mole % of oxides of additional acceptor cations selected from the group of oxides of cations consisting of Zn 2+ , Ni 2+ , Co 2+ and Co 3+ .
6. The high temperature ceramic dielectric composition of claim 1 , wherein the glass forming compound is SiO 2 .
7. A multilayer ceramic capacitor having at least one electrode buried within a body of the capacitor and an external electrode secured in electrical communication with the electrode, the body comprising:
a. about 98.35 mole % of a calcined base mixture of Me x (Bi 0.5 Na 0.5 ) 1-x TiO 3 , wherein Me is selected from the group consisting of Ba 2+ and Sr 2+ , and wherein X is from between about 0.06 and about 0.12;
b. about 0.88 mole % of at least one oxide of small donor cations, the at least one oxide of small donor cations including an oxide of at least one of Nb 5+ , Ta 5+ , and W 6+ small donor cations;
c. about 0.38 mole % of at least one oxide of acceptor cations;
d. about 0.13 mole % of oxides of large donor cations selected from the group consisting of Nd 2 O 3 , other rare earth oxides, and combinations thereof; and,
e. about 0.26% mole % of a glass forming compound selected from the group consisting of SiO 2 , Ge0 2 , V 2 0 5 , and combinations thereof.
8. The multilayer ceramic capacitor of claim 7 , wherein the oxides of small and large donor cations are selected from the group of oxides of small and large donor cations consisting of Nb 5+ , Ta 5+ , and W 6+ .
9. The multilayer ceramic capacitor of claim 7 , wherein the oxides of small and large donor cations are selected from the group of oxides of small and large donor cations consisting of Nb 5+ , Ta 5+ , W 6+ , La 3+ , Pr 3+ , Sm 3+ , Gd 3+ and Ce 4+ .
10. The multilayer ceramic capacitor of claim 7 , wherein the about 0.38 mole % of at least one oxide of acceptor cations includes about 0.09 mole % of MnO.
11. The multilayer ceramic capacitor of claim 7 , wherein the about 0.38 mole % of at least one oxide of acceptor cations includes about 0.09 mole % of MnO and about 0.29 mole % of oxides of additional acceptor cations selected from the group of oxides of cations consisting of Zn 2+ , Ni 2+ , Co 2+ and Co 3+ .
12. The multilayer ceramic capacitor of claim 11 further comprising the capacitor having a dielectric constant of between about 3600 and about equal to or greater than 4000, with dielectric losses of less than 1% over a temperature range from about 150° C. to about 300° C., at a measurement frequency of 1 KHz and 1 VRMS.
13. The multilayer ceramic capacitor of claim 11 further comprising the capacitor having changes of dielectric constant of less than about plus or minus 15% over an operating temperature range of about 150° C. to about 300° C.
14. The multilayer ceramic capacitor of claim 11 further comprising the capacitor having dielectric constant/voltage characteristics wherein the dielectric constant changes are less than about 20% over an operating temperature range of about 150° C. to about 300° C. whenever a bias of up to 40 volts direct current is applied at dielectric thicknesses of about 0.001 inch (0.02540 mm).
15. The multilayer ceramic capacitor of claim 7 , wherein the body of the capacitor consists essentially of:
a. about 98.35 mole % of a calcined base mixture of Me x (Bi 0.5 Na 0.5 TiO 3 , wherein Me is selected from the group consisting of Ba 2+ and Sr 2+ , and wherein X is from between about 0.06 and about 0.12;
b. about 0.88 mole % of at least one oxide of small donor cations;
c. about 0.38 mole % of at least one oxide of acceptor cations;
d. about 0.13 mole % of oxides of large donor cations selected from the group consisting of Nd 2 O 3 , other rare earth oxides, and combinations thereof; and,
e. about 0.26% mole % of a glass forming compound selected from the group consisting of SiO 2 , B 2 0 3 , Ge0 2 , V 2 0 5 , and combinations thereof.
16. A high temperature ceramic dielectric composition suitable for use within a capacitor, the composition comprising:
a. about 98.35 mole % of a calcined base mixture of Me x (Bi 0.5 Na 0.5 ) 1-x TiO 3 , wherein Me is selected from the group consisting of Ba 2+ and Sr 2+ , and wherein X is from between about 0.06 and about 0.12;
b. about 0.88 mole % of oxides of small donor cations selected from the group of oxides of cations consisting of Nb 5+ , Ta 5+ , and W 6+ ;
c. about 0.09 mole % of MnO yielding acceptor cations;
d. about 0.13 mole % of oxides of large donor cations selected from the group consisting of Nd 2 O 3 and other rare earth oxides;
e. about 0.29 mole % of oxides of additional acceptor cations selected from the group of oxides of cations consisting of Zn 2+ , Ni 2+ , Co 2+ and Co 3+ ; and,
f. about 0.26% mole % of a glass forming compound selected from the group consisting of SiO 2 , B 2 0 3 , Ge0 2 , V 2 0 5 , and combinations thereof.
17. The high temperature ceramic dielectric composition of claim 16 , wherein the glass forming compound is SiO 2 .