Development of Neutron 4-circle Diffractometer for studies of Structural Phase Transition

我们在东海JRR3M-JAERI(日本研究堆)的导馆里研制了一台用于单晶实验的四圆衍射仪。衍射仪的名字改为FINDER(四圆偏心式衍射仪)。我们还研制了一种硅板水平和垂直弯曲单色矿。用9块Si422板，在样品位置成功地获得了尺寸为1 cm×2 cm的聚焦良好的中子束。此时的中子波长为1.54A，样品的最大散射角为156度。我们研究了方酸、MeHPLN等氢键材料，CuGeO_3、氧化铁电体和反铁磁性化合物YMn_2O_5等氧化物材料，得到了它们的结构和相变方案。我们还研究了氟化锰MnF_2的结构和磁性结构，得到了很好的R因子，并获得了带有自旋的电子密度。最大熵法和傅里叶合成法在核密度计算中取得了很大的成功。现在可以用中子进行结构分析了。

We have developed a 4-circle diffractometer for a single crystal experiment at the guidehall of the reactor JRR3M-JAERI (Japanese Research Reactor) at Tokai. The name of the diffractometer was adapted as FONDER (Four-Circle Off-center Type Diffractometer). We also developed a horizontally and vertically bend monochromatore with silicon plates. We could succeed to get well-focused neutron beam as a size of 1cm times 2cm at the sample position by using nine Si422 plates. Wavelength of the neutron is 1.54A at the moment and the maximum scattering angle of a sample is 156 degree. We investigated several hydrogen bond materials like squaric acid and MeHPLN, oxide materials such as CuGeO_3, an oxide ferroelecric and antiferromagnetic compound YMn_2O_5, and obtained their structure and the phase transition scheme. We also studied structure and magnetic structure of manganese fluoride MnF_2. Very good R-factor was obtained, and electron density which is carrying spins was obtained. Maximum entropy method and Fourier synthesis methods were applied to btain nuclear density with great success. Structure analysis with neutron is now available.