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

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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.