Gupta, S P Sen

Kar, T

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Indian J. Phys. 72A (1), 83-86 (1998)NOTEI J P  A- an international journalH ardness an iso tropy  of L -arg in ine phosphate m onohydrate (LA P) crystalT Kar and S P Sen GuptaDepartment of Materials Science, Indian Association for the Cultivation of Science, Jadavpur. Calcutta-700 032, IndiaReceived 23 July 1997. accepted 24 September 1997Abstract : Deformation characteristics of an important non-linear material, l.-arginine phosphate monohydrate (LAP) was studied by measuring the anisotropy of Knoop microhardness on (100) cleaved plate of LAP for various loads It was found that the low load deformation is mainly due to the slip system (100) <011> whereas the higher load deformation is dominated by twinningKeywords : L-arginine phosphate monohydrute. Knoop microhardness PACS No. : 46.30.PaL-arginine phosphate monohydratc (LAP) with Lhe chemical formula [H2N]+CNH(CH2)3 CH|NH3rCOO“H2PO^H20 » *s a promising nonlinear optical (NLO) material discovered by Chinese scientists Xu el al f 1 ]. The attractive features of this material arc its hi^h damage threshold (> 15 j/cm 2 at 20 ns), large nonlinearity (> ! pm/V) and the ease with which large crystals of high optical quality can be grown [2,3]. So, it has the potential to replace potassium dihydrogen phosphate (KDP), the material most commonly used for frequency conversion of infrared lasers in the harmonic frequency generation for laser fusion experiments. As a part of our project work on this important NLO crystal, we have already reported the growth and characterization of LAP [4], In the present note, we report the anisotropy of Knoop microhardness on (100) cleaved plate of LAP.For these studies, a (100) cleaved plate of LAP grown in this laboratory, was taken and polished with water to make the test face flat. A mhp 160 microhardness tester, fitted with a Knoop mdentor and attached to a Carl-Zeiss (Jenavert) incident light research microscope, was used for the measurement of microhardness. The hardness anisotropy was measured by applying a minimum of five indentations for each load at an interval of 15° and over the range of 0-165°. The zero degree orientation of the long Knoop indentor© 1998 I ACS72A<1)-1284 T K ar and S P Sen Guptadiagonal is parallel to [0101 and was established by the macrosteps that form along the direction [0101 [5]. The load was varied from 10 gm to 50 gm and the indentation period was kept constant at 10 S. Owing-to the microcracks at the corners of the impression, the maximum load applied was 50 gm. The Knoop hardness was calculated from the usual formula |6JHK = 0.014228 x P /d 2 gm m irr2using the known lest load P (gm) and the measured length d (mm) of the long diagonal of the indentationFigure 1 shows the Knoop microhardness (HK) measured on the cleavage (100) plane of LAP with 10 gm normal load in air at different orientations of the indentor. Rotating the crystal from 0° to 165°, hardness was found to decrease from a high of 66.40L o r~ 60X8 ®cH  40|  30 _* 0Figure I. V anal ion of Knoop iiiiciohardnL*«»s iH^) with imlentor onenlalionon lhe (100) cleavage plane ol L-angmine phosphate monohydrate (L AP) at10 gm load *at 0° to a low of 31.31 at 45° and then there is a further increase in hardness upto 150°, though no sharp maximum is found in between.Figure 2 shows the load dependence of the Knoop microhardncss for the two indentor orientations [010) and [011J on the ( 100) plane. Initially, the hardness number (Hk) decreases with load for both indentor orientations and maintains a constant ratio upto P = 20 gm, that is the relative microhardness apparently is independent of load in this range. But in the high load region above P = 20 gm, the difference in hardness number (HK) between the two orientations becomes more pronounced and also the hardness number increases for 10 11J orientation upto a load P = 50 gm, but for [010] orientation the variation of HK is slightly different from that of [011] orientation. The result is found disputable with the observations made by different investigators on different crystals which generally have shown that the microhardness either increase or decrease with load al low loads and subsequently attains a fixed value at higher loads. The explanation for this type of behaviour observed here is due to the different types of slip systems that are operative with increase in load. To get a clear understanding of this behaviour, an additional study of15 30\>- J _ _ _ _ l - . .45 60 50 105 120 135Indentor Orientation (degrees)150 165Hardness anisotropy o f  L-arguune phosphate etc 85hardness anisotropy at 50 gm load was undertaken and it was observed that the variation in hardness at this test load is somewhat different from that with load 10 gm (Figure 1) The variation of Knoop microhardness (HK) at different orientations of the indenlor on cleavageFigure 2. Vanalion ol Knoop microhardness (H^) wiih load (/J) on the (10(1) cleavage plane ol L-anginine phosphate monohydrate (LAP) for two different orientations ol indenlor ()°-0, I J V -J(100) plane of LAP for these two loads 10 gm and 50 gm is presented in Figure 5. This shows different degrees ol plastic deformation by twinning and slip at the two loads. TheFigure 3. Variation of Knoop microhardness (Hr ) with indenlor orientation on the (100) cleavage plane of L-anginine phosphate monohydrate (LAP) at 10 gm (O) and 50 gm (x) loadslow load deformation is mainly caused by slip where as the higher load deformation is dominated by twinning. The low load hardness anisotropy could be explained by slip on the (100) [011 ] system.In conclusion, plastic deformation in organic nonlinear optical crystal LAP occurs as a result of either slip or twinning and the relative contribution depends on the magnitude ofload.86 T Kar and S P Sen GuptaReferencesD  Xu. M J m a n g  and  Z  Tan Ada ('hem Sintra 41 5 7 0  (1983)| 2 |  I) E im e r l .  S Ve lsko ,  L Davis,  F W a n g ,  G  L o ia c o n o  a n d  G  K e n n e d y  IEEE J Quantum Electron. QE-2S 170 M O T )131 S P V e ls k o  and  D  Em ier l  Pun Soi Thoto-Opi Instrum Engg 8 9 5  152 (1 088)|4J A M a / u m d a i ,  T  K a r  and  S P Sen G u p ia  Jjm J Appl Pirn 3 4  5717  (1 995)15] G D hanara i ,  I Shripathi  and  H I -H h a t  J. Cryst Growth 113 4 5 6  (1 991)|6J B W  Mott  Micro-Indentation Hardness Testing (L o n d o n  . Bu t le rw o rth s)  2 0 6  (1 956)

Hardness Anisotropy of L-Argimne Phosphate Monohydrate (LAP) Crystal

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Hardness Anisotropy of L-Argimne Phosphate Monohydrate (LAP) Crystal

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