计算钙钛矿结构

Experimental

Materials Synthesis:The SBA-15template was prepared by adding 4.0g tri-block copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol)(E O20PO70EO20)to a solution of 25g(35wt.-%)HCl and125g water under stirring.After stirring for 2h,the copolymer was completely dissolved,after which8.6g TEOS was added.Following continuous stirring for20h at35 C,the reac-tion mixture was transferred to a Teflon-lined autoclave and heated at 100 C for24h.The resulting product was obtained by filtration, washed repeatedly with a large amount of water,air-dried at room temperature,and calcined at500 C for6h to remove the surfactant. The calcined SBA-15was used as template for the preparation of mesoporous carbon CMK-3by CVD as follows:0.3g of calcined SBA-15was placed in an alumina boat and inserted into a flow-through tube furnace.Under a flow of nitrogen saturated with styrene vapor at room temperature,the temperature of the furnace was increased,at a ramp rate of20 C min±1,to the final pyrolysis/carbon-ization temperature(in the range850±1050 C)and maintained for 3h under the styrene-saturated nitrogen atmosphere.The furnace was then cooled to room temperature and the resulting SBA-15/car-bon mesophase was thoroughly washed with hydrofluoric acid(HF) to etch out the silica.For comparison we also prepared a CMK-3sam-ple via liquid impregnation(designated CMK-3I)using the method of Jun et al.[4].Sucrose was used as carbon source and carbonization was performed at900 C for7h[4].The mesoporous carbon was then recovered by etching the silica in HF.We also prepared CMK-3sam-ples using other carbon sources,e.g.,acetonitrile. Characterization:Powder XRD analysis was performed using a Philips1830powder diffractometer with Cu K a radiation(40kV, 40mA).Nitrogen sorption isotherms and textural properties of the materials were determined at±196 C using nitrogen in a conventional volumetric technique by a Coulter SA3100sorptometer.Before anal-ysis,the samples were oven dried at150 C and evacuated for12h at 200 C under vacuum.The surface area was calculated using the Brunauer±E mmett±Teller(BE T)method based on adsorption data in the partial pressure(P/P0)range0.05±0.2,and the total pore volume was determined from the amount of the nitrogen adsorbed at P/P0»0.99.The micropore surface area and micropore volume were obtained via t-plot analysis.SEM images were recorded using a JEOL JSM-820scanning electron microscope.Samples were mounted using a double-sided conductive carbon sticky tape.A thin(ca.10nm)coat-ing of gold sputter was deposited onto the samples to reduce the effects of charging.Thermogravimetric analysis of the silica/carbon (i.e.,SBA-15/CMK-3)composite materials was performed using a Perkin Elmer Pyris6TG analyzer(heating rate of20 C min±1)in static-air conditions.

Received:November11,2003

Final version:March10,2004±

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2815.

A Novel Approach to Synthesizing Calcium Copper Titanate Thin Films with Giant Dielectric Constants**

By Raffaella Lo Nigro,Roberta G.Toro,

Graziella Malandrino,Marco Bettinelli,

Adolfo Speghini,and Ignazio L.Fragalà*

The field of microelectronics has developed rapidly over the last fifteen years,and its evolution is documented by the continuously improving performances of logic and memory devices,as well as by the number of components per chip. Nevertheless,the continuing effort towards device miniaturi-zation is often frustrated by limitations due to some physical properties of current materials.In particular,in the case of memory devices based on capacitive components,the static dielectric constant will decide the level of miniaturization.[1] This has spurred intriguing investigations either on novel materials or on novel properties of already known materials that have never been thought of for a particular application. Many materials currently used as capacitors in microelec-tronics are ferroelectric,[2]and possess a perovskite-based structure.Thus,BaTiO3,Pb(Zr,Ti)O3,and(Ba,Sr)TiO3[3,4]are well known for their high dielectric constants.However,they suffer from high instability upon temperature variation.On

±

[*]Prof.I.L.Fragalà,R.G.Toro,Dr.G.Malandrino

Dipartimento di Scienze Chimiche,Universitàdi Catania,and INSTM UdR Catania,Viale A.Doria6,I-95125Catania(Italy)

E-mail:lfragala@dipchi.unict.it

Dr.R.Lo Nigro

IMM,sezione di Catania,CNR

Stradale Primosole n50,I-95121Catania(Italy)

Prof.M.Bettinelli,Dr.A.Speghini

Dipartimento Scientifico e Tecnologico,Universitàdi Verona

and INSTM

UdR Verona,Ca'Vignal,Strada Le Grazie15,I-37134Verona(Italy) [**]This work has been partially supported by MIUR(Ministero dell'Is-truzione,dell'Universitàe della Ricerca)under progetto Fondo Inte-grativo Speciale per la Ricerca(FISR).The authors thank Mr.Corra-do Bongiorno of the IMM CNR of Catania for assisting with the TEM observations.