Dynamics of structural and magnetic phase transitions in ferroborate YFe3(BO3)(4)

X-ray analysis of the YFe₃(BO₃)₄ single crystal revealed different behavior of parameters of the crystal cell with an increase in temperature from 25 to 500 K. The parameters a and b initially increase monotonically and then rise sharply in the range between 360 and 380 K, which corresponds to the structural phase transition. The parameter c initially decreases linearly upon heating and then begins to increase, passing through a minimum at 90 K. In the interval of 200–500 K the parameter c grows linearly and does not undergo anomalies at the structural phase transition. The results of Mössbauer measurements at ⁵⁷Fe nuclei in the paramagnetic phase of YFe₃(BO₃)₄ correlate well with the XRD data, but they do not separate the two structural states of iron ions Fe1 and Fe2 arising in the P3₁21 phase during the structural phase transition. The temperature of the magnetic phase transition T_N = 39.42(16) K is established, below which the iron ions form a 3D magnetic order of the Heisenberg type. The calculated “Mössbauer” Debye temperature Θ_M = 340(2) K turned out to be three times lower than the Debye temperature of the entire crystal lattice T_D = 1020 K. Mössbauer data indicate a weak bonding between the helicoidal chains of iron and the rest of the crystal lattice.