A Novel Reaction Path to BaTiO₃ by the Oxidation of a Solid Metallic Precursor

Abstract

Multilayer capacitors with thin, dielectric BaTiO, layers can possess a relatively high capacitance per unit volume. A solid metallic precursor method has recently been developed for preparing thin BaTiOJnoble metal laminates. In the present paper, the phase and microstructural evolution of Ba-Ti metallic precursors were examined after oxidation at 300" to 900°C in pure oxygen at 1 atm pressure. Barium peroxide, BaO,, formed rapidly during oxidation at 300"C, with titanium largely remaining as unoxidized particles in the peroxide matrix. Between 375" and 500"C, the solidstate reaction of barium peroxide with metallic titanium yielded barium orthotitanate, Ba,TiO,. Further exposure to temperatures between 500" and 900°C resulted in the oxidation of residual metallic titanium. The oxidized titanium then reacted with the orthotitanate matrix to form barium metatitanate, BaTiO,. The rate of formation of BaTiO, was found to be strongly dependent on the degree of milling of the Ba-Ti precursors and on the heating rate between 300" and 500°C.

The Reaction‐Bonded Aluminum Oxide Process: I, The Effect of Attrition Milling on the Solid‐State Oxidation of Aluminum Powder

“…1,2 A number of reaction-based processes have been developed to produce metal oxide materials including directed metal oxidation, DIMOX ™ , solid metallic precursor (SMP), and the reaction-bonded aluminum oxide (RBAO) process. [3][4][5][6][7][8] The RBAO process involves heating a compact of attritionmilled aluminum and ␣-alumina powder in an oxidizing atmosphere to produce ␣-alumina-based components. 8 During heating, the Al particles undergo oxidation by either a solid-gas or liquid-gas reaction at temperatures Ͻ1100°C, depending on the reaction temperature (T m,Al ϭ 660°C), to produce an aluminabased matrix which then sinters to high density at Ͼ1400°C.…”

Combustion syntheses for BaTi4O9and PbxBa1–xTi4O9

“…This means they can be hotpressed to ceramic forms. 38 BaTi 5 O 11 is also a low temperature compound that is stable up to 1100 ± C. 32 The XRD of Pb 0.5 Ba 0.5 Ti 4 O 9 calcined at 700 ± C for 24 h did not change at all. The peaks of TiO 2 (rutile) are much weaker than those of BaTi 5 O 11 and PbTiO 3 because titanium is a much lighter element than barium or lead.…”

The oxidative transformation of solid, barium-metal-bearing precursors into monolithic celsian with a retention of shape, dimensions, and relative density

“…24,[26][27][28] A variety of methods have been used to produce celsian powder, including hydrothermal syntheses, [29][30][31] ion exchange of alkali feldspars, 32 and firing of solid salt mixtures. [45][46][47][48][49][50][51][52][53][54][55] An alternate, powder metallurgy-based method [56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71] for fabricating shaped bodies of celsian, or other alkaline-earth-bearing ceramic compounds, is illustrated schematically in Fig. The organic material can then be removed by pyrolysis, and the resulting porous ceramic body can be sintered to a high density at elevated temperatures (i.e., typically at >1550 ± C 17,18,24,[26][27][28]39 ).…”

“…[57][58][59]63,65,68,70,71 For example, cold rolling of a mixture of 79 vol % ductile barium with 21 vol % titanium (i.e., a precursor to BaTiO 3 ) has yielded continuous, 25 mm thick Ba-Ti tapes. [59][60][61][64][65][66]68,69 For example, a 1 cm length of a sheathed Ba-Nd 2 O 3 -CeH 3 precursor tape, in which the precursor was directly exposed to oxygen only at the end edges of the tape, was completely oxidized during a 3 h heatup from room temperature to 300 ± C. 65 The barium within a 1.6 cm length of a sheathed Ba-Ti precursor tape (i.e., with the Ba-Ti core exposed only at the end edges of the tape) was completely oxidized within 10 h in flowing oxygen at 300 ± C. 64 Such low-temperature oxidation is a consequence of the formation of porous, nonprotective oxide scales on AE metals, which, in turn, has been attributed to a significant reduction in molar volume upon oxidation (i.e., the molar volumes of magnesium, calcium, strontium, and barium are larger than the molar volumes of the corresponding oxides). 70,71 After deformation, the oxidation of AE metals, [73][74][75][76][77] and the subsequent formation of AEbearing compounds, can be conducted at relatively rapid rates and/or modest temperatures.…”

“…[59][60][61][64][65][66]68,69 For example, a 1 cm length of a sheathed Ba-Nd 2 O 3 -CeH 3 precursor tape, in which the precursor was directly exposed to oxygen only at the end edges of the tape, was completely oxidized during a 3 h heatup from room temperature to 300 ± C. 65 The barium within a 1.6 cm length of a sheathed Ba-Ti precursor tape (i.e., with the Ba-Ti core exposed only at the end edges of the tape) was completely oxidized within 10 h in flowing oxygen at 300 ± C. 64 Such low-temperature oxidation is a consequence of the formation of porous, nonprotective oxide scales on AE metals, which, in turn, has been attributed to a significant reduction in molar volume upon oxidation (i.e., the molar volumes of magnesium, calcium, strontium, and barium are larger than the molar volumes of the corresponding oxides). Indeed, the oxidation of Ba-bearing precursors at <300 ± C in pure, flowing oxygen has yielded barium peroxide, BaO 2 , which has, in turn, been found to react with other oxide or metal phases to form appreciable amounts of barium aluminate, cerate, cuprate, ferrite, titanate, or silicate compounds at <550 ± C. [59][60][61][64][65][66]68,69 Perhaps the most interesting and unusual feature of this AE-metal-bearing precursor process is the potential for producing ceramic bodies that retain the shape and dimensions of the precursor. Hence, a shaped, mechanically alloyed precursor consisting of a dense, intimate mixture of fine AE metal, non-AE metal, and oxide phases can be transformed at modest temperatures into a finely divided mixture of oxides.…”