Experimental

(CeO2)0.8(GdO 1.5)0.2 powder was synthesised from Ce(NOj)3 (99.9% Janssen) and Gd(N03)3 (99.9% Aldrich) using a reverse strike co-precipitation technique. The correct stoichiometric amounts of the nitrates were weighed and dissolved in distilled water and stirred for 20 mins. An aqueous oxalic acid (BDH) solution, with a concentration of 0.05M, was then added dropwise into the precipitant (which had been adjusted to pH 6.7 - 6.9) and stirred at 750rpm. The precipitate was then filtered and washed using distilled water (5x), followed by ethanol washing (5x), drying at 50°C (12 hours) and calcining at 700*C/lhr. Milling was performed using a Retsch centrifugal ball mill SI, with a porcelain jar and partially stabilized zirconia (PSZ) milling media. Milling was performed on the caleined powders for 15min„ followed by 12hr. drying.

The calcined powders were fabricated into bars (30 x 10 x 3mm) using a standard die press, followed by isostatic pressing (stansted fluid power ltd FPG 2347) at 200MPa. The samples were tl^en sintered in air at between 1550 - 1650"C/15 hrs. The surfaces and edges of all samples were ground using SiC grinding paper (320# - 4000#) followed by polishing (1pm diamond paste). After polishing, all the samples were annealed at 1000'C/2hr. to remove induced residual stresses. The samples (both powder and sintered bars) were examined using a Philips X-pert powder x-ray diffractometer, from room temperature to 1000'C. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDAX) were performed using a Hitatchi S4000 SEM and a Kevex microanalyser attached to the SEM, respectively. Coated samples were examined using either carbon deposition (for EDAX) analysis or rf sputtered gold. Density measurements were performed using the standard Archimedes method.

An Instron 4204 Universal tensile tester, with IEEE-48 interface controlled by an IBM 386 computer, was used for all the flexure testing. 4-point bend tests were performed using a top cross-head span of 10mm and support span of 20mm. A strain gauge (Instron 2630 - 021) was used in these tests to measure the deflection of the beam. All tests were performed at 0.2mm/min. The high-temperature tests were performed using a specially designed furnace integrated into the Instron tester. All samples were heated at a rate of 200"C/hr. and allowed to stabilize for 2hr. before starting the test. A minimum of 8 samples were examined for each test performed.

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