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This paper reports an experimental study of the heat capacity and crystal lattice parameters of a polycrystalline sample of yttrium diboride prepared by high-temperature synthesis from elements. The electronic and lattice contributions to the heat capacity are isolated. The temperature dependences of the characteristic temperature, the linear thermal expansion coefficients αa(T) and αc(T), the bulk thermal expansion coefficient β(T), and the Gruneisen coefficient are calculated. A region of negative values of αc(T) and β(T) is revealed. Anharmonicity is found to exert only a minor effect on the YB2 lattice dynamics over a larger part of the temperature range covered.

The discovery of superconductivity in MgB2 sparked much interest in the diborides and led to further discoveries in this class of materials. Attention has focussed on the transitions metal diborides and the rare-earth diborides have remained sparsely investigated. Here we present electrical transport in polycrystalline samples of ErB2, TmB2 and HoB2 as a function of temperature down to 0.1 K. Particularly interesting is the large difference in the temperature dependence of resistivity, above and below the clear magnetic ordering temperature of 13.8, 9 and 7.5 K for ErB2, HoB2 and TmB2 respectively.

Heat capacity at constant pressure C p (T) of a dysprosium boride DyB62 single crystal obtained by zone melting was studied experimentally in the temperature range of 2 to 300 K. Abnormally high values of dysprosium boride heat capacity were revealed in the range of 2–20 K, due to the magnetic contribution and the effect of disorder in the boride lattice. Temperature changes in DyB62 enthalpy, entropy, Gibbs energy, and standard values of these thermodynamic functions were calculated.

A two-step process has been proposed for the preparation of refractory rare-earth diborides: high-temperature high-pressure elemental synthesis followed by argon annealing. Using this process, we have synthesized terbium, erbium, thulium, and lutetium diborides containing no more than 3 wt % impurity phases.

Heat capacity C p(T) of dysprosium diboride is experimentally investigated at the temperatures of 5–300 K. On the dependence C p(T) smooth anomaly at the temperatures of 15–20 K and sharp anomalies at T m1=47.8 K and T m2=178.8 K are revealed. Anomaly at T m1 is caused, obviously, by ferromagnetic phase transition in DyB2. The lattice contribution to DyB2 heat capacity is determined by comparison with heat capacity of non-magnetic YB2. The estimation of Schottky contribution to DyB2 heat capacity is made, the scheme of splitting of the ground state of Dy3+ ion is offered.

The heat capacity at constant pressure C p (T) of terbium diboride synthesized from elements via an intermediate hydride phase was studied experimentally within 5–300 K. A ferromagnetic phase transition manifests itself in the C p (T) dependence as a sharp maximum at 142.4 ± 0.1 K. The C p (T) dependence was used to calculate the tempreature dependences of the enthalpy, entropy, and the Gibbs energy and to determine the parameters of the electronic, lattice, and magnetic contributions to the heat capacity of TbB2.

Temperature dependences of heat capacity and lattice parameters of gadolinium tetraboride (GdB4) at the temperatures of 2–300 K have been studied experimentally. In the course of the experiment, the anomalies of these properties caused by the processes of transition into the antiferromagnetic state at TN = 41.87 K were revealed. Temperature changes of electronic and lattice, the magnetic contribution to GdB4 heat capacity, as well as the Schottky contribution were singled out and analyzed. Residual entropy of the Gd3+ magnetic subsystem caused by frustration was found to be Rln3.2. Temperature variations of linear and volumetric thermal expansion coefficients were calculated. It was established that processes of magnetic ordering in GdB4 give rise to a negative spontaneous magnetostriction and are not accompanied by the distortion of the crystalline lattice.

The temperature dependences of heat capacity, C p (T) , and lattice parameters, a(T) , b(T) , c(T) , of ErB 50 in the temperature range of 2–300 K were experimentally studied. Two features in C p (T) were observed: a maximum at T m1 = 3.12 K, that is associated with a magnetic ordering (transition to an antiferromagnetic state), and a broad anomaly at about T m2 = 27 K that is due to the effects of the crystal electric field (CEF) on the boride heat capacity. Based on these data a scheme of splitting of Er 3+ ions f-levels by the crystal field was suggested. Comparison of the temperature dependence of unit cell volume V(T) for ErB 50 with the literature data for LuB 50 revealed an excess contribution into the thermal expansion of erbium boride at low temperatures. It was determined that this contribution is due to the CEF effects on ErB 50 thermal expansion.