Potassium Dihydrogen Phosphate with High Quality

• CAS No.: 7778-77-0
• Color: White
• Appearance: Powder
• Transport Package: Paper
• Specification: large
• Trademark: china
• Model NO.: E1422
• Origin: China
• HS Code: 2930400000
• Production Capacity: 5000kg/Year

Product Description

Potassium dihydrogen phosphate and its isomorphs are representative of hydrogen-bonded materials that possess important piezoelectric, ferroelectric, electrooptic, and nonlinear optical properties. Since the first report of the ferroelectric properties of KDP by Bush and Scherrer in 1935, numerous studies on their electrical and optical properties have been reported. They have attracted the interests of many theoretical and experimental researchers, probably because of their comparatively simple structure and very fascinating properties associated with a hydrogen bond system involving a large isotope effect. A very conspicuous feature in the development of the physics of these crystals is the close interplay between theory and experiment which makes significant progress in the understanding of their microscopic properties possible.

A crystallochemical analogue of KDP, NH₄H₂PO₄ found fairly wide practical applications and is used as a piezoelectric transducer in microphones, gramophones, and other sound reproduction devices. The very first materials to be used and exploited for their nonlinear optical and electro-optical properties were KDP and ADP. They were used in the first experiments in nonlinear optics, and together with their isomorphs, they are still used widely in nonlinear optical devices and continue to be popular as electro-optic materials. Compared with other isomorphs of the KDP family, KDP and ADP have found wide practical applications.

KDP belongs to the class 4¯ 2 m of the tetragonal system with the space group I4¯ 2 d. The unit cell dimensions are a=b=7.434 Å and c=6.945 Å. There are four formula units per cell. The structure is most easily pictured as built up from potassium atoms and phosphate groups as shown in Fig. 1.

 

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Figure 1. Structure of KDP.

The structure consists of two interpenetrating body-centered lattices of PO₄ tetrahedra and two interpenetrating body-centered K lattices, the phosphate and potassium lattices being separated along the c-axis. Every PO₄ is linked to four other PO₄ groups by hydrogen bonds which lie very nearly perpendicular to the ferroelectric c-axis. The linkage is such that there is a hydrogen bond between one upper oxygen of one PO₄ group and a lower oxygen of a neighboring group. As revealed by the neutron studies only two hydrogens are normally located nearest any one PO₄ group, giving rise to a ionic configuration K⁺(H₂PO4−).

KDP has a phase transition to ferroelectric from its paraelectric state at 123 K whereas ADP has an antiferroelectric phase transition from its paraelectric state at 148 K. Though ADP is isomorphous with KDP at room temperature, the cell dimensions are markedly different; a=b=7.5006 Å and c=7.5490 Å. The projection of the structure onto the b, c plane is shown in Fig. 2.

 

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Figure 2. The (100) projection of the ADP structure.

It can be seen that ADP differs from KDP by having extra NHO hydrogen bonds, which connect the PO₄ tetrahedra with a neighboring NH₄ group. Each oxygen atom is connected to another oxygen atom in the neighboring PO₄ ion and with a nitrogen atom in a neighboring NH₄ ion by two kinds of bonds: OHO and NHO. According to the positional refinements of each atom in ADP by x-ray diffraction study, both above and below the phase transition point, each NH₄ ion at the potassium position in the KDP structure is shifted to the off-center position by forming two shorter and two longer bonds with four PO₄ tetrahedra in the low-temperature phase. When oxygen is connected with the shorter NHO bond, it tends to keep the other proton off in the OHO bond and when it is connected with the longer NHO bond it tends to take the acid proton nearby. Thus the extra hydrogen bonds produce a distorted NH₄ ion lattice at low temperature and cooperate with the acid protons in causing proton configurations different from those found at low temperature in KDP. The properties of KDP and its isomorphs are listed in Table 1.

Table 1. Properties of KDP and its isomorphs.

Empty Cell	KH2PO4 (KDP)	KD2PO4 (KD*P)	NH4H2PO4 (ADP)	ND4H2PO4 (AD*P)
Crystal data		99 at.% D		99 at.% D
Crystal symmetry and class	Tetragonal, 4¯ 2m	Tetragonal, 4¯ 2m	Tetragonal, 4¯ 2m	Tetragonal, 4¯ 2m
Space group	I 4¯ 2d	I 4¯ 2d	I 4¯ 2d	I 4¯ 2d
Lattice constants (Å)	a=7.4529 c=6.9751	a=7.4697 c=6.9766	a=7.4991 c=7.5493	a=7.5193 c=7.5400
Cleavage	None	None	None	None
Hygroscopic susceptibility	High	High	High	High
Density (gcc^−1)	2.3325	2.3555	1.799	1.885
Optical properties
Transmission region >50% Sample thickness 2 mm thick	0.176-1.55 μm	<0.2-2.15 μm	0.184-1.5 μm	<0.2 to >2.0 μm
Indices of refraction (in 22 °C air)
0.266 μm	no=1.5599 ne=1.5105	no=1.5539 ne=1.5071	no=1.5797 ne=1.5261	no=1.5701 ne=1.5191
0.532μm	no=1.5129 ne=1.4709	no=1.5071 ne=1.4683	no=1.52775 ne=1.4815	no=1.5211 ne=1.4776
0.6328μm	no=1.5079 ne=1.4673	no=1.50285 ne=1.4648	no=1.5222 ne=1.4773	no=1.5163 ne=1.47365
1.064μm	no=1.4944 ne=1.46035	no=1.4934 ne=1.4583	no=1.5068 ne=1.4681	no=1.5052 ne=1.4658
dn/dT(10^−6 °C^−1) (20-40 °C)
0.266 μm	dno/dT=−38 dne/dT=−29	dno/dT=−37 dne/dT=−24	dno/dT=−52 dne/dT=−2	dno/dT=−24 dne/dT=+2
0.532μm	dno/dT=−40 dne/dT=−29	dno/dT=−37 dne/dT=−24	dno/dT=−56 dne/dT=−2	dno/dT=−28 dne/dT=+2
1.064μm	dno/dT=−48 dne/dT=−31	dno/dT=−44 dne/dT=−24	dno/dT=−81 dne/dT=−3	dno/dT=−24 dne/dT=+5
NLO susceptibility d36 (10^−2 mV^−1)
0.6943μm	0.70	0.53	0.85	0.77
1.064μm	0.63	0.42	0.762	-
Electrical properties
Resistivity (10^6 ohm-cm)	10-20	10	10-20	10
Piezoelectric coefficients (pC/N)
d14	1.3	3.4∼98 at.% D	1.8	10∼98 at.% D
d36	21	58∼99 at.% D	48.3	75∼99 at.% D
Electromechanical coupling factors
k14	0.008	-	0.006	-
k36	0.121	0.22	0.33	-