Sensors zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA and Actuators A, 37-38 (1993) 375-378 375 Piezoelectric and thermoelectric re$ponse of cuprous oxide, Cu,O Victor Chang INTEVEP S A , Research and Development Center, AJihate of Petroleos de Venezuela, P 0 Box 74343, Caracas 1070 A (Venezuela) Humberto RoJas and Jose Jorge UruversrdadCentral de Venezuela, Escuela de Frrrca, Caracas (Venezuela) Abstract In the present work, polycrystaihne samples of cuprous oxide, Cu,O, are fabncated and their plezoelectnc and thermoelectnc propertles evaluated both as a polycrystalhne matenal and as a composite matenal Samples are prepared from electrical or analytical grade copper, m powder or sohd form Oxldatlon IS carned out at 1050 “C for 4 h For the polycrystalhne form, the Seebeck coefficient IS about 1 mV/T For the composite form, the c&Lent IS between 0 2 and 0 4 mV/T A plezoelectnc response IS also found For the polycrystallme material, the ratio between generated voltage and applied voltage IS about 0 2 at the resonance frequency For the composite samples, this ratio hes between 0 01 and 0 02 Resonance frequencies are m the range 150 kHz-20 MHz, dependmg on the specific sample The mentioned properties are not greatly dependent on gram size or gram onentafion, probably due to the cubic structure of the Cup0 elemental cell Intduction The thermoelectnc and plezoelectnc properties of matenals are wdely used m the fabncatlon of sensors In the past, cuprous oxide, CuzO, has been used as a semiconductor for recttfiers and as a matenl for solar cells However, its thermoelectnc and plezoelectnc re- sponses as a sensor matenal have not been reported [I] The purpose of the present work was to fabncate and evaluate such propeties, both m the crystal form and as a composite matenal The crystal presents a cubic structure composed of oxygen atoms and copper atoms disposed as shown m zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 0 *42696A l cu 00 Rg I Cu,O elemental cell Numbers mdlcate the position of atoms m the cube Fig 1 Copper IS widely used as a raw material, since it 1s cheap and easily available compared to other sensor matenals The Cu,O fabrlcatlon techmque 1s simple and the oxide stable However, one of its mam dlsad- vantages 1s the frag&ty of the crystal Experimental Preparatw n of Cu,O crystals The crystals were prepared from metalhc copper of analytical quahty and electrical quahty, m sohd or powder form For the oxldatlon process, the technique of Toth et al [2] was used, mod&d to utlhze ambient pressure [ 31 In order to avold formmg cupnc oxide, graphite was used as a reducmg agent, placed with copper mslde an alumma container Powdered ahnnma was used to fab- ncate moulds m which the Cu,O crystals do not adhere to the walls A programmable furnace was adjusted to a heatmg rate of 1200 “C/h The oxidation temperature was 1050 “C for 24 h Vanable oxldatlon tnnes, between 4 and 100 h, were tested m order to study the gram-size growth Sample preparatron Due to the fragMy of the polycrystals, samples were embedded m epoxy resin pnor to producmg parallel faces by mcchamcal tnmmmg The faces were placed at different angles m relation to the crystal-growth dlrec- tlon A thm layer of conductive resin (ESL) was placed 09244247/93/36 00 @ 1993 - Elsewer Sequoia All nghts reserved