X-ray and Neutron Studies of Antiferroelectric Phase Transition in Cu(HCOO) 2 ·4H 2 O

Abstract

X-ray diffraction and incoherent inelastic neutron scattering studies are performed to clarify the phase transition mechanism of Cu(HCOO) 2 ·4H 2 O. Contrary to the previous electrical study, we find no evidence of the existence of an intermediate ferrielectric phase. We determine the accurate antiferroelectric structure. It turns out that the atomic arrangement of the Cu(HCOO) 2 layers remains unchanged through the phase transition, while the antiferroelectric H 2 O layers take one of two disordered paraelectric arrangements alternately along the c-axis. We discuss that the rotation of the H 2 O molecules induces the structural correlation one-dimensionally along the antiferroelectric b-axis.

Incoherent Inelastic Neutron Scattering Study of Antiferroelectric Cu(HCOO) 2 ·4H 2 O Crystal

“…We found that some peaks lying in the range of 1 ¼ 65 -90 meV become broad above T t ¼ 235:5 K: The modes in this energy range can be assigned empirically to the out-ofplane H 2 O librational modes. Considering the structure of the H 2 O layer [2], we conclude that the disorder of the H 2 O layer in the PE phase is induced by the rotation of the H 2 O molecules with the out-of-plane hydrogen motion.…”

“…Figure 1 shows the AFE structure which is formed by two kinds of layers; an H 2 O layer and a Cu(HCOO) 2 layer. The crystal structure analysis has revealed that the H 2 O layer is disordered above T t and ordered below T t , while the Cu(HCOO) 2 layer remains practically unchanged through T t [2]. This indicates that the phase transition of CFT can be regarded as that of "quasi-two-dimensional ice".…”

Effect of pressure on two-dimensional Heisenberg antiferromagnet Cu(HCOO)2·4H2O

“…The single crystals of CFT were grown by slow cooling an aqueous solution from about 40 1C at a rate of 1 1C/day [4]. The DC susceptibility and magnetization measurements of the single crystal and powder samples were calculated using a superconducting quantum interference device (SQUID) magnetometer (Quantum Design MPMS-5S).…”

Synthesis, Crystal Structures, Magnetic, and Thermal Properties of Divalent Metal Formate–Formamide Layered Compounds.

“…Formate, the smallest carboxylic ligand, was studied several decades ago because of the unusual physical properties observed in hydrated transition metal formate compounds. , A renewed interest in formate based frameworks has occurred recently . The formate ligand adopts different bridging modes depending on the coordination environment .…”

“…Thus, the neighboring metal centers are effectively coupled via the formate bridging ligand leading to interesting magnetic behavior. The structure–property relationship of hydrated transition metal formates M (HCOO) 2 · x H 2 O ( M = transition metals) and their deuterated forms, ,, anhydrous metal formates [ M (HCOO) 2 ], metal formates with monodentate ligands [ M (HCOO) 2 ·2L] (L = urea), metal formates with bidentate ligands [ M (HCOO) 2 L] (L = 4,4′-bipyridine, pyrazine), and metal formates with solvents [ M (HCOO) 2 · n (solvent)] have been studied. In many of these compounds the behavior of the magnetic susceptibility below the Néel temperatures suggested weak ferrimagnetism.…”