(JP2000226260-A)   NOVELTY - An LaGaO3 sintered body comprises lanthanum, gallium, oxygen, and at least one of other elements, and has at least three crystal phases of different composition formulae.    USE - LaGaO3-based sintered body, for oxygen-permeable membrane, a reactor, a sensor device. Can be used as an electrolyte of a solid electrolyte fuel cell.    ADVANTAGE - A LaGaO3 sintered body having improved mechanical strength is obtained without impairing the high electrical conductivity. A sensor device is provided with a reduced interfacial resistance between an oxide ion-conducting solid electrode and a noble metal electrode and therefore exhibits greatly improved oxygen pumping ability and works satisfactorily even in temperatures of 700 degreesC or lower.    (JP2000292408-A)   NOVELTY - An LaGaO3 sintered body comprises lanthanum, gallium, oxygen, and at least one of other elements, and has at least three crystal phases of different composition formulae.    USE - LaGaO3-based sintered body, for oxygen-permeable membrane, a reactor, a sensor device. Can be used as an electrolyte of a solid electrolyte fuel cell.    ADVANTAGE - A LaGaO3 sintered body having improved mechanical strength is obtained without impairing the high electrical conductivity. A sensor device is provided with a reduced interfacial resistance between an oxide ion-conducting solid electrode and a noble metal electrode and therefore exhibits greatly improved oxygen pumping ability and works satisfactorily even in temperatures of 700 degreesC or lower.    (JP2000351669-A)   NOVELTY - An LaGaO3 sintered body comprises lanthanum, gallium, oxygen, and at least one of other elements, and has at least three crystal phases of different composition formulae.    USE - LaGaO3-based sintered body, for oxygen-permeable membrane, a reactor, a sensor device. Can be used as an electrolyte of a solid electrolyte fuel cell.    ADVANTAGE - A LaGaO3 sintered body having improved mechanical strength is obtained without impairing the high electrical conductivity. A sensor device is provided with a reduced interfacial resistance between an oxide ion-conducting solid electrode and a noble metal electrode and therefore exhibits greatly improved oxygen pumping ability and works satisfactorily even in temperatures of 700 degreesC or lower.