Microhardness studies on as‐grown (111) faces of some alkaline earth nitrates

Abstract

Single crystals of Sr(NO 3 ) 2 , Ba(NO 3 ) 2 and Pb(NO 3 ) 2 are grown from their aqueous solutions at a constant temperature of 35 °C by slow evaporation technique. Crystals of size 8 to 10 mm along one edge are obtained in a period of 10 days. Chemical etching technique has been employed to study the dislocations in these crystals. The dislocations are randomly distributed and the dislocation density is about 10 4 to 10 5 /cm 2 . Microhardness studies are made on as-grown (111) faces of these crystals upto a load of 100 g. The hardness of the crystals increases with an increase in load and thereafter it becomes independent of the applied load. These results are discussed on the basis of reverse indentation size effect. Meyer index number n for these crystals is estimated at both low and high load regions. An analysis of hardness data of these crystals as well as some other cubic crystals like alums and alkali halates are discussed using Gilman-Chin parameter H v /C 44 , where H v is the microhardness and C 44 is the shear constant.

Optical and microhardness studies on unidirectional grown triaqua glycine sulfato zinc (II): A semiorganic NLO crystal

“…According to the indentation size effect (ISE), microhardness of crystals decreases with increasing load and in reverse indentation size effect (RISE) hardness increases with increasing load. In our case, H v increases with load up to 200 g and becomes load independent for P ≥ 200 g. Similar observation is observed in alkaline earth nitrate crystals [26]. The traditional Meyer's law gives the relationship between load P and size d [27]:…”

“…Microhardness measurement is commonly used to determine the mechanical strength of the material which is related to bond strength and defect structure [26]. Optically clear and defect free crystal plate taken perpendicular to the growth direction was subjected to indentation tests at room temperature.…”

Enhancement of structural perfection of alkali halide single crystals by doping with copper

“…The initial increase in microhardness (H v ) is due to reverse indentation size effect (ISE). Similar observations were made on a number of crystals like alkaline earth nitrates [17], Bi 2 Te 3 [18], (NH 4 ) 2 SO 4 [19] and GaTe [20]. The Cu þ doped crystals are less harder than the pure crystals KCl:Cu þ (8.8 kg/mm 2 ), KCl (10 kg/mm 2 ), NaCl:Cu þ (19.7 kg/mm 2 ), NaCl (25.2 kg/mm 2 ).…”

Growth and characterization of Manganese Sulpho Tartrate (MST)—A semiorganic NLO crystal

“…A well polished MST crystal of 2mm thick was placed on the platform on the Vickers microhardness tester and the loads of different magnitude were applied over a fixed interval of time. The hardness was calculated using the relation [27] H v = 1.8544 P/d 2 kg/mm 2 , where P is the applied load in gram and d is the diagonal length of the indentation impression in millimeter. The relation between hardness number (H v ) and load (P) for MST is shown in Fig 7. The hardness increases gradually with the increase of load and above 100g cracks were developed on the smooth surface of the crystal due to release of the internal stresses generated locally by indentation [28].…”