Heat capacity of solid NH3

Properties of multiferroicBiFeO3under high magnetic fields from first principles

“…One important problem that remains to be addressed in BFO is the consequence of applying large magnetic fields on the magnetic and electric sublattices, as well as on the ME coupling. As a matter of fact, while the existence of a magnetic transition that destroys the cycloidal structure in favor of a homogeneous magnetic configuration has been proposed in BFO bulks for a critical magnetic field H cyc Ӎ 20 T ͑at 20 K͒, 15,16 we are not aware of any study reporting characteristics of the magnetic ordering and its effects on polarization for fields much higher than H cyc . One may therefore wonder if not only different magnetic transitions can occur at large magnetic field, but also how such transitions ͑if any͒ depend on the direction of the applied field and how they affect the polarization.…”

Thermal conductivity of solid ammonia at low temperatures

“…For the calculations, the data of Refs. were utilized. The phonon velocity was averaged over transversal and longitudinal lattice vibrations following the expression: where is the velocity of longitudinal wave, is the velocity of transversal wave.…”

“…Comparing the dependence of thermal conductivity of solid ammonia with the dependencies of thermal conductivity of some other simple dielectric crystals (here N 2 and CH 4 ), we can see a wider as well as diffuse maximum for solid ammonia crystal. The highest value of the coefficient of solid ammonia is 4.4 W m À1 K À1 and appears at approximately 25 K. The high temperature of the maximum may be related to a relatively high, as for simple dielectric crystal, Debye temperature Q D ¼ 231 K [18] of ammonia (whereas in the case of other simple crystals of this type, such as neon, argon, krypton, nitrogen, methane it does not exceed 100 K [29]) on the one hand and a high concentration of defects of the sample structure, on the other. As was briefly noted above, the scattering of phonons by dislocations may reduce the value of the thermal conductivity coefficient and influence the functional dependence of the thermal conductivity on temperature, and due to dislocation scattering one may register k $ T 2 in the low-temperature region.…”

“…In the investigations experimental methods such as X-ray, IR, and neutron scattering were utilized [10][11][12][13][14][15][16]. Also, the thermal properties of NH 3 crystal such as specific heat and thermal expansion were investigated [17,18]. The thermal conductivity of solid ammonia was measured only at temperatures above 30 K [19,20].…”

“…For the calculations, the data of Refs. [18,33] were utilized. The phonon velocity was averaged over transversal and longitudinal lattice vibrations following the expression:…”