Magnetic and structural instabilities in the hexagonal Laves hydride ErMn2H4.6 under high-pressure

Synthesis, crystal structure and hydrogenation properties of rhenium-substituted YMn2 and ErMn2

“…A tentative phase diagram and hydrogen induced phase transitions have been reported for the cubic yttrium system YMn 2 H y [7], while a Mössbauer and X-ray diffraction study [8] of the hexagonal erbium system ErMn 2 H y revealed two hydride phases having compositions y = 4.0 and 4.6 and hydrogen desorption equilibrium pressures of <1.33 mbar and ∼0.02 bar, respectively. A high-pressure X-ray and neutron diffraction study of the latter system at the composition y = 4.6 confirmed the presence of a second C14-type phase in the pressure range 0-3 × 10 4 bar [6]. However, for none of the Er or Y systems has a complete structure determination including atomic coordinates of hydrogen (deuterium) been reported.…”

“…The volume increments generally decrease with Re content and increase with D content. In the deuterides of the Y series, for example, they decrease from 3.2 Å 3 /D at the Re poor (x = 0.54) and D rich (y = 3.44) composition Y(Mn 0.46 Re 0.54 ) 2 D 3.44 (6) to 2.8 Å 3 /D at the Re rich (x = 0.93) and D poor (y = 0.48) composition Y(Mn 0.07 Re 0.93 ) 2 D 0.48 (3) , and from 3.4 Å 3 /H for x = 0.5 (y = 3.6) to 2.4 Å 3 /H for x = 0.9 (y = 1) in the hydrides. For the Er series, the volume increments also decrease as a function of Re content from 3.6 Å 3 /H (x = 0, y = 4.8 [4]) to 2.6 Å 3 /H (x = 0.9, y = 0.8) in the hydrides.…”

“…While the yttrium member YMn 2 crystallizes with the cubic C15-type structure if prepared under normal pressure conditions [2] and with the hexagonal C14-type structure if prepared under high pressure conditions (70 kbar at T = 1573-1673 K) [3], the erbium member ErMn 2 crystallizes with only the C14-type structure [3]. The C14-type modifications of both members absorb hydrogen and have been studied with respect to structural, thermodynamic and magnetic properties [4][5][6]. A tentative phase diagram and hydrogen induced phase transitions have been reported for the cubic yttrium system YMn 2 H y [7], while a Mössbauer and X-ray diffraction study [8] of the hexagonal erbium system ErMn 2 H y revealed two hydride phases having compositions y = 4.0 and 4.6 and hydrogen desorption equilibrium pressures of <1.33 mbar and ∼0.02 bar, respectively.…”

“…Interestingly, the high-pressure phases have the stoichiometric composition RMn 2 D 6 and crystallize with a partially disordered K 2 PtCl 6 -type structure in which the R atoms and half of the Mn atoms share the same crystallographic site. The compounds can be formulated as complex metal hydrides containing MnH 6 5− anions in analogy to the FeH 6 4− anions as found in Mg 2 FeH 6 [11]. In order to stabilize these hydrides under less stringent pressure conditions and to possibly obtain ordered CaF 2 -type metal substructures such as in Mg 2 FeH 6 , we have made attempts to substitute manganese by rhenium.…”

“…1: Y(Mn0.46Re0.54)2D 3.44(6) , agreement indices: RB = 2.83%, Rp = 12.7%, Rwp = 11.1%, Chi 2 = 2.39; secondary phase Y6Mn23D23 (9.9 wt.%). Refined composition 2: Y(Mn0.40Re0.60)2D 3.46(7) , agreement indices: RB = 1.87%, Rp = 12.2%, Rwp = 11.7%, Chi 2 = 2.64; secondary phases Y2O3 (1.6 wt.%) and Y6Mn23D23 (0.6 wt.%).Refined composition 3: Y(Mn0.31Re0.69)2D 3.04(6) , agreement indices: RB = 2.69%, Rp = 11.6%, Rwp = 11.4%, Chi 2 = 2.39; secondary phases Y2O3 (1.7 wt.%) and Y6Mn23D23 (3.9 wt.%).…”