@article{AhlertFranzHohlweinetal.1995, author = {Ahlert, D. and Franz, Robert U. and Hohlwein, D. and Prandl, W. and Schiebel, P. and Siemensmeyer, K.}, title = {Die partielle Konversion von inkoh{\"a}renter in koh{\"a}rente Streuung an Protonen : das Ausfrieren der Quanten-Spin-Fluktuationen beim freien NH3-Rotator in Ni(NH3)6(PF6)2}, series = {In: Zeitschrift f{\"u}r Kristallographie / Supplement issue No. 9 (1995) , p. 82}, journal = {In: Zeitschrift f{\"u}r Kristallographie / Supplement issue No. 9 (1995) , p. 82}, pages = {82}, year = {1995}, language = {de} } @article{SchiebelAhlertFranzetal.1996, author = {Schiebel, P. and Ahlert, D. and Franz, Robert U. and Hohlwein, D. and Prandl, W. and Siemensmeyer, K. and Wulf, K.}, title = {Partial conversion of neutron incoherent into coherent scattering by NH3 quantum rotators}, series = {In: Physica B: Condensed Matter 226 (1996) 1-3, pp 234-237}, journal = {In: Physica B: Condensed Matter 226 (1996) 1-3, pp 234-237}, doi = {10.1016/0921-4526(96)00312-2}, pages = {234 -- 237}, year = {1996}, abstract = {Neutron diffraction experiments on powders are used to investigate the quantum mechanical behaviour of uniaxial rotators, i.e. NH3-molecules in Ni(NH3)6(PF6)2, Co(NH3)6(PF6)2 and Ni(NH3)6I2. A diffuse temperature dependent component of the total scattering, modulated ∼ sin QrH-H/QrH-H, is observed at a temperature of ≃ 20 K and below. This observation is due to the fact, that on cooling the sample to kT ∼ B (rotational constant) the rotational ground state is strongly populated. The ground state of a uniaxial free rotator, however, is completely polarized. As a consequence the scattering of those NH3 groups being in the ground state becomes coherent and is observable in diffraction experiments.}, language = {en} }