Mechanical properties of β-HMX

Background: For a full understanding of the mechanical properties of a material, it is essential to understand the defect structures and associated properties and microhardness indentation is a technique that can aid this understanding. Results: The Vickers hardness on (010), {011} and {110} faces lay in the range of 304-363 MPa. The Knoop Hardnesses on the same faces lay in the range 314-482 MPa. From etching of three indented surfaces, the preferred slip planes have been identified as (001) and (101). For a dislocation glide, the most likely configuration for dislocation movement on the (001) planes is (001) [100] (|b| = 0.65 nm) and for the (101) plane as (101) 101~(|b| = 1.084 nm) although (101) [010] (|b| = 1.105 nm) is possible. Tensile testing showed that at a stress value of 2.3 MPa primary twinning occurred and grew with increasing stress. When the stress was relaxed, the twins decreased in size, but did not disappear. The twinning shear strain was calculated to be 0.353 for the (101) twin plane. Conclusions: HMX is considered to be brittle, compared to other secondary explosives. Comparing HMX with a range of organic solids, the values for hardness numbers are similar to those of other brittle systems. Under the conditions developed beneath a pyramidal indenter, dislocation slip plays a major part in accommodating the local deformation stresses. © 2015 Gallagher et al.; licensee Springer

Dielectric and domain structural properties of Bi2GexV1−xO5.5−x/2Bi_2Ge_xV_{1-x}O_{5.5-x/2} single crystals

Single crystals of $Bi_2Ge_xV_{1-x}O_{5.5-x/2}$, with various concentrations of x, have been grown by slowly cooling the melts of $Bi_2O_3, V_2O_5$ and $GeO_2$ in appropriate ratios. Single crystal X-ray diffraction studies confirm their single crystallinity. X-ray powder diffraction studies carried out on crushed single crystals indicate that the compositions corresponding x=0.3 to 0.5 belong to the tetragonal system, while the remaining concentrations of x (0&les;x<0.3 and 1&ges;x>0.5) belong to the orthorhombic system. The polarising microscopic investigations revealed the existence of interesting ferroelectric domain patterns. The dielectric and ferroelectric studies have been done along the c axis of these crystal

The dielectric properties of ferroelectric bismuth vandate,Bi2 VO5.5 under pressure

The dielectric properties of single crystals and ceramics of BizV05 5 have been investigated as a function of pressure up to 4 GPa at room temperature.The dielectric constant and the loss are found to decrease with increase in pressure for all the samples under study. However. the rate of decrease of the dielectric constant in the case of partially grain oriented ceramic is higher than that of the single crystal and conventionally synthesised ceramic. The decrease in dielectric constant with increase in pressure is attributed to the decrease in ionic polarisation as a consequence of the decrease in interionic distances

Dielectric, thermal and pyroelectric properties of ferroelectric bismuth vanadate single crystals

Single crystals of $Bi_2V0_{5.5}$ (BiV) which is n = 1 member of Aurivillius family of oxides, have been grown by slowly cooling the melts of the prereacted compound. The dielectric, pyroelectric and ferroelectric properties have been studied along the c - axis as a function of temperature of the first time. The ferroelectric Curie temperature (720 K) of these single crystals is confirmed by dielectric, pyroelectric, specific heat and hysteresis loop studies. The dielectric and specific heat data obtained well beyond 720 K confirm that BiV undergoes yet another crystallographic transition at 827 K. The pyroelectric figures of merit from the point of view of different applications have been calculated at 300 K by combining pyroelectric, dielectric and thermal properties

Structural and dielectric properties of Bi2NbxV1-xO5.5 ceramics

Bi2NbxV1-xO5.5 ceramics with x ranging from 0.01 to 0.5 have been prepared. The crystal system transforms from an orthorhombic to tetragonal at x greater than or equal to 0.1 and it persists until x = 0.5. Scanning electron microscopic (SEM) investigations carried out on thermally etched Bi2NbxV1-xO5.5 ceramics confirm that the grain size decreases markedly (18 mu m to 4 mu m) with increasing x. The shift in the Curie temperature (725 K) toward lower temperatures, with increasing x, is established by Differential Scanning Calorimetry (DSC). The dielectric constants as well as the loss tangent (tan delta) decrease with increasing x at room temperature

Domain structure of Bi2GexV1−xO5.5−x/2Bi_2Ge_xV_{1-x}O_{5.5-x/2} single crystals

Experimental evidence exists that ferroelectric crys- tals consist of many domains [1]. This was proved conclusively for $BaTiO_3$ by investigating its domain structure in detail using a polarizing microscope [2, 3]. In this letter we report the domain structure obtained by polarizing microscopy for off-valent, germanium (Ge^4^+)-doped single crystals of bismuth vanadate $(Bi_2VO_{5.5})$, which is a vanadium analogue of the n = 1 member of the Aurivillius family of oxides [4-6]

Structural and dielectric properties of Bi2NbxVi−xO5.5 ceramics

Bi2Nbx V1−xO5.5 ceramics with x ranging from 0.01 to 0.5 have been prepared. The crystal system transforms from an orthorhombic to tetragonal at x 3= 0.1 and it persists until x = 0.5. Scanning electron microscopic (SEM) investigations carried out on thermally etched Bi2NbxV1−xO5.5 ceramics confirm that the grain size decreases markedly (18 μm to 4 μm) with increasing x. The shift in the Curie temperature (725 K) toward lower temperatures, with increasing x, is established by Differential Scanning Calorimetry (DSC). The dielectric constants as well as the loss tangent (tan δ) decrease with increasing x at room temperature

Pyroelectric properties of Bi2VO5.5 ceramic

The dielectric, pyroelectric and thermal properties of ferroelectric Bi2VO5.5(Bi4V2O11) ceramic have been studied over a temperature range of 300-780 K. The sign of the pyroelectric coefficient is positive at room temperature. The dielectric constant, pyroelectric coefficient and specific heat exhibit anomalies around the Curie temperature, 725 K. The frequency response of the dielectric constant and tan delta has been studied over a frequency range of 1-100 kHz. It is found that both the dielectric constant and the loss tangent decrease with increasing frequency. The pyroelectric figures of merit from the point of view of different applications have been calculated at 320 K by combining pyroelectric, dielectric and thermal properties

The effect of CrO_4\hspace{2mm}^{2-} ions on the electro-optic properties of KDP single crystals

Sufficiently large yellowish single crystals of KDP doped with various concentrations of $K_2CrO_4$ have been grown for electro-optic device applications, by the slow-evaporation Holden's rotary crystallizer technique. These crystals have been characterized for their ferroelectric and linear electro-optic properties. The doped crystals have low half-wave voltages as compared with that of pure KDP while there are no significant changes in the ferroelectric properties

High-temperature X-ray structural, thermal and dielectric characteristics of ferroelectric Bi2VO5.5Bi_2VO_{5.5}

The X-ray powder diffraction, dielectric and thermal studies of bismuth vanadate $(Bi_2VO_{5.5})$ ceramic have been carried but as a function of temperature (300-900 K). The hightemperature X-ray studies, supported by differential scanning calorimetry, clearly demonstrate that $Bi_2VO_{5.5}$ undergoes two major phase transitions at $\sim 730$ and $\sim 835 K$. It was found that the one at 730 K is associated with both the ferroelectric and the crystallographic transition, while at 835 K, $Bi_2VO_{5.5}$ undergoes only the crystallographic transition. Anomalies in both the dielectric constant and specific heat curves have been observed at ,$\sim 730$ and $\sim 835 K$. The total heat, $\Delta Q$, and entropy, $\Delta S$, associated with the transition at 730 K were found to be higher than those at 835 K