Bismuth Pyrochlore Films for Dielectric Applications

Abstract

Bismuth pyrochlore ceramics have modest temperature coefficients of capacitance, good microwave properties, and can be prepared at relatively modest temperatures (∼900 – 1100 °C). This work focuses on the preparation and characterization of thin films in this family for the first time. A sol-gel procedure using bismuth acetate in acetic acid and pyridine, in combination with zinc acetate dihydrate and niobium ethoxide in 2-methoxyethanol was developed. The solution chemistry was adjusted to prepare (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 and Bi2(Zn1/3Nb2/3)2O7 films. Solutions were spin-coated onto platinized Si substrates and crystallized by rapid thermal annealing. In both cases, crystallization occurred by 550 °C into the cubic pyrochlore structure. (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 films remained in the cubic phase up to crystallization temperatures of 750 °C, while the structure of the Bi2(Zn1/3Nb2/3)2O7 thin films is dependent of the firing temperature: cubic below 650 °C and orthorhombic above 750 °C. A mixture of cubic and orthorhombic structures is found at 700 °C. The resulting BZN films are dense, uniform, and smooth (rms roughness of < 5 nm). Cubic bismuth zinc niobate films show dielectric constants up to 150, a negative temperature coefficient of capacitance, TCC, (∼ - 400 ppm/°C), tan δ < 0.01, and a field tunable dielectric constant. Orthorhombic films showed smaller dielectric constants (∼80), low tan δ (< 0.01), positive TCC, and field independent dielectric constants. TCC could be adjusted to new 0 ppm/°C using a mixture of orthorhombic and cubic material.

Microwave and infrared dielectric response of monoclinic bismuth zinc niobate based pyrochlore ceramics with ion substitution in A site

“…2 and 3͔͒. 12,13 No dielectric relaxation was observed in monoclinic BZN, 14 which corresponds also to a better ordered crystal structure. [4][5][6][7] In cubic pyrochlore BZN the Bi and Zn atoms in the A positions are disordered among six closely spaced equivalent sites and the OЈ atoms from the A 2 OЈ tetrahedral network among 12 sites, 4 while the Zn atoms prefer the B site to the A site.…”

Surface Termination and CO2 Adsorption onto Bismuth Pyrochlore Oxides

“…The bulk structural and electronic properties of bismuth-based pyrochlore materials have been extensively studied mainly due to their general high dielectric constant and low dielectric loss, which are desirable properties in the field of electronics devising. , There is, however, a series of novel potential applications of this type of material, such as oxygen-evolution catalysis and visible-light photocatalysis, whose development largely depends on the knowledge of the surface chemistry. Pyrochlore bismuth iridates have been shown to have good activity and high stability for the oxygen evolution reaction, which is mediated by surface redox processes .…”

Phase Decomposition and Dielectric Properties of Reactively Sputtered Bismuth Zinc Niobate Pyrochlore Thin Films Deposited from Monoclinic Zirconolite Target

“…It has been reported that BZN films prepared by metal organic deposition (MOD) process [12][13][14], pulsed laser deposition (PLD) [15,16] and RF-magnetron sputtering [17][18][19] showed noticeable voltage-tunable dielectric properties. Recently, it was found that one of the most important factors for tunability is nonstoichiometry of the BZN films (especially Bi contents) when cubic BZN target is used [12,13].…”

“…Recently, it was found that one of the most important factors for tunability is nonstoichiometry of the BZN films (especially Bi contents) when cubic BZN target is used [12,13]. In this work, the dielectric-tunable properties of BZN thin films by RF-magnetron sputtering using monoclinic BZN target were investigated in terms of nonstoichiometry.…”