| abstract |
<PICT:1107305/C6-C7/1> A dielectric body has conductive regions formed therein by selective reduction. The invention is described with reference to the reduction of a crystalline compound of formula Mx Y3- x Aq Fe5- q O12, wherein M is selected from the group consisting of aluminium gallium, indium, thallium, lanthanum, scandium and the rare earth elements, and x is any number between 0 and 3; wherein A is selected from the same group of metals and q is any number between 0 and 5; and wherein x is always less than 3 when q = 5 and q is always less than 5 when x = 3; and in particular yttrium iron garnet, Y3 Fe5 O12, (YIG). Other compounds which may be used include spinels, hexagonal iron oxides, and perovskites. The degree of conductivity attained depends upon the intensity and duration of the reducing reaction. Fig. 1 shows a YIG body the surface of which has been reduced in a hydrogen atmosphere. Inner region A comprises unreduced YIG having a resistivity of about 1012 ohm-cm. while surface E consists almost entirely of metallic iron; intermediate layers B, C, D are of progressively higher conductivities. Regions of limited conductivity, e.g. to form resistors, are produced by partial reduction. Surfaces may be metallized by reduction prior to the plating thereof, e.g. with nickel, by an elctroless process. Electroless plating of nickel may be carried out in a solution containing the following percentages by weight:- .NiCl2 . 6 H2O.3% .NaH2 PO2 . H2O.1% .Ammonium chloride.5% .Sodium citrate.10% .Water.81% Ammonium hydroxide is repeatedly added to the solution during plating at 95 DEG C. for half an hour. Other metals, such as silver, may be deposited be electroless plating on the reduced surface. |