Subsolidus phase equilibria and electrical properties of pyrochlores in the Bi2O3–CuO–Ta2O5 ternary system

Abstract

Subsolidus phase relations had been determined for the Bi 2 O 3-CuO-Ta 2 O 5 (BCT) system over the temperature range 700-950 °C in air. Two structurally distinct ternary phases of different symmetries, a cubic pyrochlore and a monoclinic zirconolite were observed. Phasepure pyrochlores existed in a unique boomerang-shaped area, which could be described using the general formula, Bi 2.48+y Cu 1.92−x Ta 3.6+x−y O 14.64+3x/2−y : 0.00(1) ≤ x ≤ 0.80(1) and 0.00 (1) ≤ y ≤ 0.60(1), respectively. BCT subsolidus pyrochlores exhibited low electrical conductivities, 10 −7-10 −6 S cm −1 , moderate dielectric constants, ε′, ∼60-80 and low dielectric losses, tan δ, ∼0.01-0.20 at 1 MHz and ambient temperature, ∼28 °C. The recorded low activation energies, 0.32-0.40 eV suggesting these electroceramics were of semiconductortype at elevated temperatures.

Synthesis and Electrical Properties of Zn‐substituted Bismuth Copper Tantalate Pyrochlores

“…The impedance response may contain two main resistances, which contributed to the total resistance. 16,20 As to verify this, the capacitance, that is, 6.91 9 10 À12 F/cm at xRC = 1, represents the bulk (intragranular) capacitance 22 with e 0 of~78, while the grain boundary (intergranular) should have a capacitance in the order of nanofarads 23 . The decrease in semicircle arcs with increasing temperature signifies a decrease in total resistance, insets of Fig.…”

“…In our earlier works, phase relations for the system Bi 2 O 3 –CuO–Ta 2 O 5 have been determined over the temperature range 700–950°C in air. The subsolidus solid solution spans over a boomerang‐shaped area, which could be represented by the general formula, Bi 2.48+ y Cu 1.92− x Ta 3.6+ x − y O 14.64+3x/2− y : 0.00(1) ≤ x ≤ 0.80(1) and 0.00(1) ≤ y ≤ 0.60(1) …”

“…The subsolidus solid solution spans over a boomerang-shaped area, which could be represented by the general formula, Bi 2.48+y Cu 1.92Àx Ta 3.6+xÀy O 14.64+3x/2Ày : 0.00(1) ≤ x ≤ 0.80(1) and 0.00(1) ≤ y ≤ 0.60(1). 16 In this research, Zn is chosen as an alternative substituent for Cu as to overcome the problems of low sinterability and high dielectric loss in BCT pyrochlores. In addition, Zn cation has a comparable ionic radius, 0.74 A if compared to that of Cu 2+ (0.73 A) that fits well in the six-coordinated B site of pyrochlore.…”

“…Similar distorted semicircle arc in Cu‐containing pyrochlores suggests that there could be more than an electroactive region within these samples. The impedance response may contain two main resistances, which contributed to the total resistance . As to verify this, the capacitance, that is, 6.91 × 10 −12 F/cm at ωRC = 1, represents the bulk (intragranular) capacitance with ε′ of ~78, while the grain boundary (intergranular) should have a capacitance in the order of nanofarads.…”

Performance Differences of Ta2O5 Films under Different Magnetron Sputtering Conditions

“…Tantalum pentoxide (Ta 2 O 5 ) has a variety of uses in electricity [1] and optics [2], and it can be used as a dielectric material in capacitors [3]，in semiconductor integrated devices [4], as well as in battery and coating materials [5]. And it is also important as a dielectric material in a novel memory device [6].…”