Preparation And Microstructure Of BaHfO₃:Ce Ceramic Scintillator

BaHfO₃:Ce is a new type of ceramic scintillator materials with a simple cubic structure and high density. It is optical isotropic and has some advantages of strong ability to stop X ray, and decay time is short. BaHfO₃:Ce is a promising ceramic scintillator material suitable for the rapid response detector which can be used for the medical imaging technology , non-destructive testing and the high-energy physics. In this paper, preparation of BaHfO₃:Ce powder and microstructure of the sample in the sintering process were studied systematically, combined with Natural science of Key projects liaoning province (2005222009) and the Education department key projects of Liaoning Provincial (20040240).BaHfO₃: Ce powder were obtained, after calcining at 1000℃for 2h in the weak reductive atmosphere by the oxalic acid salt precursor which prepared by oxalate precipitation method. The phase transformation and mass losing during the calcination process, the micro-morphology and the optical properties of powder were characterized by XRD, TG-DSC, SEM , TEM and fluorescence spectrophotometer. The influence on the morphology and particle size of powder by aging time, calcination temperature and concentration of oxalic acid, and the influence on the crystal structure and the luminescent properties by the concentration of Ce³⁺ were studied. The results show that the increase of aging time is in favor of the Oswald ripening of the precipitant particle and forming big stable particles; when the concentration of oxalic acid is 0.2mol/L, particle size is about 0.25μm and it was the optium powder morphology. The doping of Ce³⁺ doesn't change the crystal structure. Powder has the optimal luminescent properties when Ce³⁺ is 0.3mol%, but the concentration quenching is accrued over 3mol%. There are two wide spectral bands under the exciting of 393nm and 445nm .In the experiment of ammonia as the precipitant, hydroxide precursor was prepared with different titration type (positive titration or reverse titration) and after calcining at 1000℃for 2h in the weak reductive atmosphere, BaHfO₃:Ce powder was obtained. The experimental results show that the metal ions can be precipitated together because of the initiate pH value is large when using the reverse titration type. Grain size is about 60nm and the powder has the optium morphology when the concentration of Ce³⁺ is 0.3mol%, Powder has the best optical properties when the Ce³⁺ doping concentration is 0.3mol%. There are also two wide spectral bands under the exciting of 393nm and 445nm.BaHfO₃:Ce powders can be easier prepaired by the ammonia precipitation method and the particle size is in the nanometer range, the microstructure and otical properties were not affected by different pricipitating agent. All of these indicated that the optimal best precipitating agent can synthesize the high sintering activity, even size BaHfO₃:Ce powders, it is the important promoter action to the preparation of BaHfO₃:Ce ceramics scintillator.The effect of embeded sintering technique and direct sintering on the sample shrinkage, the influence of the green density on the densification were studied, and the impact of the vacuum sintering or the free pressure sintering on the sintering densificaton and the grain size were under farther research. The results indicate that: the shrinkage is concentrated in 1650℃and changes of shrinkage are very small by embedded technique, but the line shrinkage is mainly concentrated in 1550-1650℃and changes of shrinkage suddenly at 1550℃with the direct sintering technique, which is easy to cause the sample cracking and distortion. When the green density is lower than 52%, the density after sintering is difficult to achieve 90%. The density of sample by vacuum sintering is above 97% at 1650℃, and the grain size is mainly in 50-60μm; but when the sintering temperature is about at 1750℃, the sinter density can be achieved by the free pressure sintering. The microstructure of the sample is offected largely by the different sintering type and the vacuum sintering is better than the free pressure sintering.