Synthesis, crystal structure and properties of YB₂C₂

Figures & data

Figure 1. DSC curve obtained with YH₂, B₄C and C mixture at a heating rate of 10 °C/min up to 1450°C under a flowing Ar atmosphere.

Figure 2. XRD patterns of mixed powders at (a) RT, and after sintering at (b) 1000 °C, (c) 1150 °C, (d) 1250 °C, (e) 1450°C.

Figure 3. ΔG and ΔH curves of dehydrogenation reaction of YH₂.

Figure 4. XRD patterns of mixed powders with a molar ratio of YH₂:B₄C:C = 1.95:0.9:2.95 after sintering at 1600°C.

Figure 5. Simulated electron diffraction patterns of the P_42c (a, b) and P4/mbm (c, d) structure along the [010] (a,c) and [001] (b,d) zone axes. Red dots in (d) show the positions of extinction diffraction spots. For the two structures, the diffraction patterns along [100] are identical to those along [010] and not provided here for brevity. Experimental selected area electron diffraction patterns along [010] (e), [1_10] (f) and [001] (g). Convergent beam electron diffraction pattern along [001]. The green and pink lines denote the mirror planes.

Figure 6. Powder XRD spectra of YB₂C₂: observed spectrum (the × black dotted line), Rietveld generated spectrum (the red upper solid line) and difference between the two (the bottom purple solid line). The blue vertical ticks below the pattern represent possible bragg reflections of YB₂C₂.

Table 1. Calculated (cal.) and experimental (Obs.) data of reflections, 2θ positions and intensity for YB₂C_2.

Reflection(hkl)	2θObs.(^o)	2θCal.(^o)	d Obs.(Å)	d Cal.(Å)	I/I0Obs.(%)	I/I0 Cal. (%)
1 1 0	23.59	23.53	3.77	3.77	63.5	54.5
0 0 1	25.08	25.01	3.55	3.56	17.7	14.2
2 0 0	33.56	25.98	2.69	3.426	21.5	24.1
1 1 1	34.66	34.60	2.59	2.59	100	100
2 1 0	37.90	37.61	2.37	2.38	0.3	0.2
2 0 1	42.31	42.26	2.13	2.13	46.1	49.5
2 2 0	48.15	48.13	1.89	1.88	12.5	12.9
0 0 2	51.37	51.32	1.78	1.78	13.7	14.1
3 1 0	54.26	54.24	1.69	1.68	17.9	23.01
2 2 1	55.01	54.98	1.67	1.67	12.2	18.3
1 1 2	57.23	57.2	1.61	1.61	13.1	13.9
3 1 1	60.64	60.58	1.53	1.52	12.0	16.5
3 2 0	62.73	62.67	1.48	1.48	8.6	10.7
4 0 0	70.43	70.42	1.34	1.33	1.5	2.7
2 2 2	73.00	72.94	1.30	1.29	5.8	9.2
3 3 0	75.41	75.35	1.26	1.29	1.2	1.7
4 0 1	76.04	75.98	1.25	1.30	5.6	7.6
3 1 2	77.93	77.89	1.23	1.22	10.6	12.3
4 1 1	78.16	78.41	1.22	1.21	4.7	2.1

Table 2. Comparison of lattice constants of YB₂C₂ derived from first-principles calculation, Rietveld refinement, electron diffraction, and from literature.

Lattice parameters (nm)	a	b	c
First-principles calculation	0.5353	0.5353	0.3593
Rietveld refinement	0.5351	0.5351	0.3561
Electron diffraction	0.531	0.531	0.354
Reckeweg′s result [6]	0.5333	0.5333	0.3546

Figure 7. (a) Total and projected electronic density of states (DOS) of YB₂C₂; (b) Mulliken population and bond length of chemical bonds in YB₂C₂; (c) pressure dependence of lattice constants a and c; (d) relative bond-length contractions for YB₂C₂ at various pressures.

Table 3. Second order elastic constants c_ij, anisotropic Young’s modulus ex and E_z, bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio of YB₂C_2.

Second order elastic constants (cij) and anisotropic Young’s modulus of single crystal
c11	c12	c13	c33	c44	c66	Ex	Ez
494	204	24	204	72	176	410	202
Elastic moduli of polycrystalline YB2C2
B		G		E		ν
140		103		249		0.20

Figure 8. Dependence of the retained flexural strength of YB₂C₂ and several other structural ceramics on the quenching temperature.

Figure 9. (a) TG curve of YB₂C₂ at 100–1300 °C; (b) XRD patterns of the YB₂C₂ sample surface after quenching at 800°C and 1300 °C; (c) SEM morphology of the YB₂C₂ sample surface after quenching at 800 °C; (d) SEM morphology of the YB₂C₂ sample surface after quenching at 1300 °C; (e) is a partial enlargement of (d); (f) SEM morphology of the cross-section of the YB₂C₂ sample after quenching at 1300°C.

Reckeweg O, DiSalvo FJ. Different structural models of YB2C2 and GdB2C2 on the basis of single-crystal X-ray data. Zeitschrift für Naturforschung B. 2014;69(3):289–293. doi: 10.5560/znb.2014-3333

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