Ceramic ferroelectric composite materials with enhanced electronic properties BSTO-Mg based compound-rare earth oxide

• US 6,074,971 A
• Filed: 11/13/1998
• Issued: 06/13/2000
• Est. Priority Date: 11/13/1998
• Status: Expired due to Term

• Current Assignee: Blackberry Limited
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Synowczynski, Jennifer, Stowell, Steven, Sengupta, Louise C., Sengupta, Somnath, Chiu, Luna H.
• Primary Examiner(s): GROUP, KARL E
• Application Number:
  US09/191,546
• Time in Patent Office: 578 Days
• Field of Search: 501/137, 501/139
• US Class Current: 501/139
• CPC Class Codes: C04B 35/053 Fine ceramics
• CPC Class Codes: C04B 35/465 based on alkaline earth metal titanates

Abstract

Ceramic ferroelectric composite materials comprising barium strontium titte/magnesium and oxygen-containing compound composite further doped with rare earth (lanthanide) oxides. More particularly, these inventive composites are comprised of Ba_1-x Sr_x TiO₃ /Mg--O based compound/rare earth oxide composite, wherein x is greater than or equal to 0.0 but less than or equal to 1.0, and wherein the weight ratio of BSTO to Mg compound may range from 99.75-20 wt. % BSTO to 0.25-80 wt. % Mg compound, and wherein said rare earth oxide additive comprises less than about 10 mole percent of the composite. The rare earth oxides of the composite include all oxides of the lanthanide series elements including scandium and yttrium, as well as combinations thereof. The magnesium-based compound may be selected from the group consisting of MgO, MgZrO₃, MgZrSrTiO₃, MgTiO₃, and MgCO₃. This new class of composite materials has enhanced electronic properties including: low dielectric constants; substantially decreased electronic loss (low loss tangents); increased tunability; increased temperature stability; decreased sintering temperatures; and low curie temperatures. The electronic properties of these new materials can be tailored for various applications including phased array antenna systems, capacitors, transmission wire, wireless communication, and pyroelectric guidance devices.

Claims

1. A ceramic ferroelectric composite material, comprising:

(a) barium strontium titanate, said barium strontium titanate represented as Ba_1-x Sr_x TiO₃, wherein x is greater than 0.0 but less than 0.7;

(b) a compound containing both magnesium and oxygen; and

(c) a rare earth oxide or a combination of rare earth oxides;

wherein said barium strontium titanate, said magnesium containing compound, and said rare earth oxide or combination thereof are combined in said composite material.

2. The ceramic ferroelectric composite material of claim 1, wherein said barium strontium titanate is Ba_1-x Sr_x TiO₃ and wherein x=0.35 to 0.45.

3. The ceramic ferroelectric composite material of claim 1, wherein said magnesium containing compound is selected from the group consisting of MgO, MgZrO₃, MgZrSrTiO₃, MgTiO₃, and MgCO₃.

4. The ceramic ferroelectric composite material of claim 1, wherein said magnesium containing compound comprises MgO.

5. The ceramic ferroelectric composite material of claim 1, wherein said rare earth oxide is selected from the group consisting of scandium oxide, yttrium oxide, lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, promethium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide, lutetium oxide, and combinations thereof.

6. The ceramic ferroelectric composite material of claim 5, wherein said rare earth oxide is selected from the group consisting of lanthanum oxide, cerium oxide, and neodymium oxide.

7. The ceramic ferroelectric composite material of claim 1, wherein the weight ratio of said barium strontium titanate to said magnesium compound ranges from about 99.75-20 percent by weight barium strontium titanate to about 0.25-80 percent by weight magnesium compound;

and wherein said rare earth oxide is added to said barium strontium titanate and magnesium compound material at a molar percentage of less than about 10 mole percent.

8. The ceramic ferroelectric composite material of claim 7, wherein said magnesium compound is selected from the group consisting of MgO, MgZrO₃, MgZrSrTiO₃, MgAl₂ O₄, MgTiO₃, and MgCO₃.

9. The ceramic ferroelectric composite material of claim 8, wherein said magnesium compound comprises MgO.

10. The ceramic ferroelectric composite material of claim 7, wherein said rare earth oxide is selected from the group consisting of scandium oxide, yttrium oxide, lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, promethium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide, lutetium oxide, and combinations thereof.

11. The ceramic ferroelectric composite material of claim 10, wherein said rare earth oxide is selected from the group consisting of lanthanum oxide, cerium oxide, and neodymium oxide.

12. The ceramic ferroelectric composite material of claim 7, wherein said weight ratio of said barium strontium titanate to said magnesium compound is approximately 40 percent by weight barium strontium titanate to approximately 60 percent by weight magnesium compound.

13. The ceramic ferroelectric composite material of claim 12, wherein said magnesium compound comprises MgO.

14. The ceramic ferroelectric composite material of claim 12, wherein said barium strontium titanate comprises Ba₀.6 Sr₀.4 TiO₃.

15. The ceramic ferroelectric composite material of claim 12, wherein said barium strontium titanate comprises Ba₀.55 Sr₀.45 TiO₃.

16. The ceramic ferroelectric composite material of claim 12, wherein said rare earth oxide is added to said material at a molar percentage of about 0.5 mole percent.

17. The ceramic ferroelectric composite material of claim 12, wherein said rare earth oxides are selected from the group consisting of scandium oxide, yttrium oxide, lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, promethium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide, lutetium oxide, and combinations thereof.

18. The ceramic ferroelectric composite material of claim 17, wherein said rare earth oxide is selected from the group consisting of lanthanum oxide, cerium oxide, and neodymium oxide.

19. The ceramic ferroelectric composite material of claim 1, wherein said material has a room temperature dielectric constant of from about 79 to about 166.

20. The ceramic ferroelectric composite material of claim 1, wherein said material has a loss tangent of less than 0.0008 at a frequency of 250 kHz.

21. The ceramic ferroelectric composite material of claim 1, wherein said material has a loss tangent of less than 0.04 at a frequency of 10 GHz.

22. The ceramic ferroelectric material of claim 1, wherein said material has a curie temperature of less than about -50°

C.

23. The ceramic ferroelectric material of claim 1, wherein said material has a tunability of greater than 4.0 percent.

24. The ceramic ferroelectric material of claim 1, wherein said material has a temperature stability of TCP_ppm in the range of 150 to 2000 ppm.