Hugoniot measurements on the highly dense, pure B4C polycrystal were performed by the inclined-mirror method to study the elastoplastic transition and to search phase transition. In inclined-mirror streak photographs, the smoothly jagged structure was observed at the free-surface shape in the plastic region. The Hugoniot-elastic limit (HEL) has been determined to be approximately 19.5GPa. In the plastic region, a kink was observed at a particle velocity of around 1.26km∕s. The shock velocity (US)–particle velocity (UP) Hugoniot relations in the plastic region were given by US=3.7+5.4UPkm∕s in the Up range of 0.54–1.26km∕s and US=9.61+0.73UPkm∕s in the Up range of 1.26–4.3km∕s. The S value (0.73) in US=C0+SUP above UP=1.26km∕s is significantly small compared with the result of Vogler et al. [J. Appl. Phys. 95, 4173 (2004)], and was much smaller than those of many oxides and nitrides. This material behaved as an elastoisotropic solid above the HEL and showed a large and linear change in the pressure-density plot above 38GPa (UP=1.26km∕s), which indicated the onset of a phase transition.

Ultrasonic velocity in glasses denoted by the composition formula x 2 Li2 O·(1-x 2) B2 O3 (x 2 is the mole fraction) is measured over the composition range 0≤x 2≤0.28 at 10 MHz and 298 K by the ultrasonic pulse-echo overlap method. The elastic property of the glasses is analyzed in terms of the three structural units defined as BØ3≡ a , Li+BØ2O-≡ b and Li+BØ- 4≡ c , where Ø represents a bridging oxygen and O- a nonbridging oxygen, on the assumption that these have their respective elastic constants defined on the basis of the elastic internal energy due to deformation. It is shown in particular that the structural unit a is converted only into the structural unit c by the reaction 2BØ3+Li2O→2Li+BØ- 4 in the composition range 0≤x 2≤0.28.

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Ultrasonic velocities in sodium borate glasses are measured as a function of composition at a frequency of 10 MHz and at a temperature of 298 K by making use of the ultrasonic pulse echo overlap method. Elastic properties of these glasses are analysed in terms of the elastic internal energy due to deformation; elastic resistances of the network-former, B203, and the modifier, Na20, are obtained as a function of composition from the plot of MV 2 against x 2, where M is the molar mass of sodium borate glasses, Vthe velocity of sound and x2 the mole fraction of NazO. The elastic resistances of B203 and Na20 are as follows: (i) for x2<0.33, the elastic resistance of B203 is smaller than that of N a20; (ii) at x2=0.33, the elastic resistances of B203 and Na20 are equal; (iii) for x2>0.33, the elastic resistance of B203 iS greater than that of Na20; (iv) at x2,,~0.15, the elastic resistances of B203 and Na20 become respectively maximal and minimal; (v) at x2,,~0.23, the elastic resistances of B203 and Na20 become respectively minimal and maximal; (vi) above x 2 = 0.36, the elastic resistance of Na20 becomes negative.

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