Electrical Behavior and Microstructural Features of Electric Field-Assisted and Conventionally Sintered 3 mol% Yttria-Stabilized Zirconia

Abstract

ZrO 2 : 3 mol % Y 2 O 3 (3YSZ) polycrystalline pellets were sintered at 1400 • C and by applying an alternating current (AC) electric field at 1000 • C. An alumina sample holder with platinum wires for connecting the sample to a power supply was designed for the electric field-assisted sintering experiments. The apparent density was evaluated with the Archimedes technique, the grain size distribution by analysis of scanning electron microscopy images, and the electrical behavior by the impedance spectroscopy technique. Sintering with the application of AC electric fields to 3YSZ enhances its ionic conductivity. An explanation is proposed, based on the dissolution back to the bulk of chemical species, which are depleted at the grain boundaries, leading to an increase in the oxygen vacancy concentration. For the enhancement of the grain boundary conductivity, an explanation is given based on the diminution of the concentration of depleted chemical species, which migrate to the bulk. This migration leads to a decrease of the potential barrier of the space charge region, known to be responsible for blocking the oxide ions through the intergranular region. Moreover, the heterogeneity of the distribution of the grain sizes is ascribed to the skin effect, the tendency of the AC current density to be largest near the surface, decreasing towards the bulk.

Microstructural evolution of 3YSZ flash‐sintered with current ramp control

“…The electrical parameters of the FS, for example, the electric field and electric current density, can significantly affect the characteristics of the sintered material . At certain values of these parameters, the grain size distribution in the sample may be heterogeneous …”

“…The grain size heterogeneity has been attributed due to several reasons: a gradient of temperature on the sample due to heat transfer mechanisms during FS; the electric current preferential path forming hotspots, resulting in localized enhancement of grain growth; difference on grain growth kinetics between the cathode and anode vicinities …”

“…[5][6][7][8][9][10][11] At certain values of these parameters, the grain size distribution in the sample may be heterogeneous. 10,[12][13][14] The grain size heterogeneity has been attributed due to several reasons: a gradient of temperature on the sample due to heat transfer mechanisms during FS 12,15,16 ; the electric current preferential path forming hotspots, resulting in localized enhancement of grain growth 13,14,17,18 ; difference on grain growth kinetics between the cathode and anode vicinities. 19,20 The properties of materials are related to their microstructure; therefore, knowledge of the grain growth kinetics associated with different FS parameters is essential.…”

Flash Sintering Samaria-Doped Ceria–Carbon Nanotube Composites

“…Electric field-assisted pressureless sintering, usually named flash sintering when the phenomenon occurs in few seconds, has been successfully applied to several inorganic compounds since it was first reported in 2011 [1]; for example in ZrO 2 : 3 mol% Y 2 O 3 [1][2][3][4][5][6], ZrO 2 : 8 mol% Y 2 O 3 [7][8][9][10][11], ZrO 2 : 20 mol% Sc 2 O 3 [12], CeO 2 : 20 mol% Sm 2 O 3 and CeO 2 : 20 mol% Gd 2 O 3 [13][14][15][16][17][18], BaCe 0.8 X 0.2 O 3-δ (X=Y, Sm, Gd) [19,20], BaTiO 3 [21][22][23], BiFeO 3 [24], CaCu 3 Ti 4 O 12 [25], ZnO [26][27][28], SnO 2 [29,30], Al 2 O 3 [31,32], SrTiO 3 [33,34], ThO 2 [35], UO 2 [36,37], TiO 2 [38], SiC [39], Y 2 O 3 [40]. The flash sintering method consists of applying a DC or AC electric field to a ceramic green compact either under heating (dynamic flash sintering) or at a temperature usually below the conventional sintering temperature (isothermal flash sintering) [41].…”

Towards In-Situ Electron Microscopy Studies of Flash Sintering

“…The flash phenomenon has been observed in many different inorganic compounds. A few recent examples include: Al 2 O 3 [5,6]; TiO 2 [7]; BaTiO 3 [8,9]; doped CeO 2 [10][11][12][13]; ZrO 2 : 3 mol% and 8 mol% Y 2 O [1, [14][15][16]; SnO 2 [17]; and ZnO [18][19][20][21][22][23][24][25].…”