Abstract: In the production of low-thermal-expansive zirconyl phosphate ceramic, whose chemical formula is (ZrO).sub.2.P.sub.2 O.sub.7 and whose chemical composition is 2ZrO.sub.2.P.sub.2 O.sub.5 by sintering of the fine-powder compact, three kinds of reaction aids are employed. They are a densifying aid, a grain-growth-suppressing aid and a solid-solution-forming aid. The densifying aid is always employed, the grain-growth-suppressing aid is employed for producing a more thermal-resistant ceramic for high temperature use and the solid-solution-forming aid is employed for producing a more low-thermal-expansive ceramic.

Abstract: A pyroelectric infrared sensor for use in intrusion alarm systems, including a pyroelectric ceramic element provided with two pairs of electrodes, of which the front electrodes are so configured as to permit a simplified printing process for higher productivity and lower production costs. The front electrodes each have a first region overlapping with a part of one of the back electrodes and a second region overlapping with a part of the other of the back electrodes, and are arranged adjacent to each other and are electrically insulated from each other. The first regions and the second regions of the front electrodes have a ratio of areas of approximately 1:1. The pyroelectric element is attached to a holding member which is so designed that the back electrode areas of the element are free from physical contact with any thermally conductive solid material that may detract from the thermal responsiveness of the element.